diff --git a/DocumentService.Client/Clients/BaseDocumentClient.cs b/DocumentService.Client/Clients/BaseDocumentClient.cs
new file mode 100644
index 0000000..76600c5
--- /dev/null
+++ b/DocumentService.Client/Clients/BaseDocumentClient.cs
@@ -0,0 +1,179 @@
+using Microsoft.Extensions.Logging;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+
+namespace DocumentService.Client.Clients;
+
+/// <summary>
+/// Base class for all DocumentService HTTP clients.
+/// Provides common HTTP operations and error handling.
+/// </summary>
+/// <remarks>
+/// 
+/// </remarks>
+/// <param name="HttpClient"></param>
+/// <param name="logger"></param>
+/// <exception cref="ArgumentNullException"></exception>
+public abstract class BaseDocumentClient(HttpClient HttpClient, ILogger logger)
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    protected readonly ILogger Logger = logger ?? throw new ArgumentNullException(nameof(logger));
+
+    /// <summary>
+    /// Sends a multipart/form-data POST with a single file and deserializes the JSON response.
+    /// </summary>
+    protected async Task<TResponse?> SendMultipartAsync<TResponse>(
+        string endpoint,
+        Stream fileStream,
+        string fileName = "file.pdf",
+        CancellationToken cancellationToken = default)
+    {
+        using var content = new MultipartFormDataContent();
+        var streamContent = new StreamContent(fileStream);
+        streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
+        content.Add(streamContent, "file", fileName);
+
+        var response = await HttpClient.PostAsync(endpoint, content, cancellationToken);
+        response.EnsureSuccessStatusCode();
+
+        return await response.Content.ReadFromJsonAsync<TResponse>(cancellationToken);
+    }
+
+    /// <summary>
+    /// Sends a multipart/form-data POST with a single file and returns the response as a stream.
+    /// </summary>
+    protected async Task<Stream> SendMultipartForStreamAsync(
+        string endpoint,
+        Stream fileStream,
+        string fileName = "file.pdf",
+        CancellationToken cancellationToken = default)
+    {
+        using var content = new MultipartFormDataContent();
+        var streamContent = new StreamContent(fileStream);
+        streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
+        content.Add(streamContent, "file", fileName);
+
+        var response = await HttpClient.PostAsync(endpoint, content, cancellationToken);
+        response.EnsureSuccessStatusCode();
+
+#if NETFRAMEWORK
+        return await response.Content.ReadAsStreamAsync();
+#else
+        return await response.Content.ReadAsStreamAsync(cancellationToken);
+#endif
+    }
+
+    /// <summary>
+    /// Sends a multipart/form-data POST with a single file and returns the raw byte array.
+    /// </summary>
+    protected async Task<byte[]> SendMultipartForBinaryAsync(
+        string endpoint,
+        Stream fileStream,
+        string fileName = "file.pdf",
+        CancellationToken cancellationToken = default)
+    {
+        using var content = new MultipartFormDataContent();
+        var streamContent = new StreamContent(fileStream);
+        streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
+        content.Add(streamContent, "file", fileName);
+
+        var response = await HttpClient.PostAsync(endpoint, content, cancellationToken);
+        response.EnsureSuccessStatusCode();
+
+#if NETFRAMEWORK
+        return await response.Content.ReadAsByteArrayAsync();
+#else
+        return await response.Content.ReadAsByteArrayAsync(cancellationToken);
+#endif
+    }
+
+    /// <summary>
+    /// Sends a caller-built <see cref="MultipartFormDataContent"/> and returns the response as a stream.
+    /// Use this overload when the multipart body contains more than one file (e.g., merge).
+    /// </summary>
+    protected async Task<Stream> SendMultipartContentForStreamAsync(
+        string endpoint,
+        MultipartFormDataContent content,
+        CancellationToken cancellationToken = default)
+    {
+        var response = await HttpClient.PostAsync(endpoint, content, cancellationToken);
+        response.EnsureSuccessStatusCode();
+
+#if NETFRAMEWORK
+        return await response.Content.ReadAsStreamAsync();
+#else
+        return await response.Content.ReadAsStreamAsync(cancellationToken);
+#endif
+    }
+
+    /// <summary>
+    /// Serializes <paramref name="request"/> as JSON, POSTs it, and deserializes the response.
+    /// </summary>
+    protected async Task<TResponse?> SendJsonAsync<TRequest, TResponse>(
+        string endpoint,
+        TRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        var response = await HttpClient.PostAsJsonAsync(endpoint, request, cancellationToken);
+        response.EnsureSuccessStatusCode();
+
+        return await response.Content.ReadFromJsonAsync<TResponse>(cancellationToken);
+    }
+
+    /// <summary>
+    /// Serializes <paramref name="request"/> as JSON, POSTs it, and returns the response as a stream.
+    /// </summary>
+    protected async Task<Stream> SendJsonForStreamAsync<TRequest>(
+        string endpoint,
+        TRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        var response = await HttpClient.PostAsJsonAsync(endpoint, request, cancellationToken);
+        response.EnsureSuccessStatusCode();
+
+#if NETFRAMEWORK
+        return await response.Content.ReadAsStreamAsync();
+#else
+        return await response.Content.ReadAsStreamAsync(cancellationToken);
+#endif
+    }
+
+    /// <summary>
+    /// Serializes <paramref name="request"/> as JSON, POSTs it, and returns the raw byte array.
+    /// </summary>
+    protected async Task<byte[]> SendJsonForBinaryAsync<TRequest>(
+        string endpoint,
+        TRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        var response = await HttpClient.PostAsJsonAsync(endpoint, request, cancellationToken);
+        response.EnsureSuccessStatusCode();
+
+#if NETFRAMEWORK
+        return await response.Content.ReadAsByteArrayAsync();
+#else
+        return await response.Content.ReadAsByteArrayAsync(cancellationToken);
+#endif
+    }
+
+    /// <summary>Converts a byte array to a Base64 string.</summary>
+    protected static string ToBase64(byte[] bytes) => Convert.ToBase64String(bytes);
+
+    /// <summary>Reads a stream fully into a byte array.</summary>
+    protected static async Task<byte[]> StreamToBytesAsync(Stream stream, CancellationToken cancellationToken = default)
+    {
+        if (stream is MemoryStream ms)
+            return ms.ToArray();
+
+        using var memoryStream = new MemoryStream();
+#if NET8_0
+        await stream.CopyToAsync(memoryStream, cancellationToken);
+#else
+        await stream.CopyToAsync(memoryStream);
+#endif
+        return memoryStream.ToArray();
+    }
+}
diff --git a/DocumentService.Client/Clients/PdfAttachmentClient.cs b/DocumentService.Client/Clients/PdfAttachmentClient.cs
new file mode 100644
index 0000000..21bb9f5
--- /dev/null
+++ b/DocumentService.Client/Clients/PdfAttachmentClient.cs
@@ -0,0 +1,124 @@
+using DocumentService.Client.Interfaces;
+using DocumentService.Client.Models.Requests;
+using Microsoft.Extensions.Logging;
+using System.IO.Compression;
+using System.Net.Http;
+
+namespace DocumentService.Client.Clients;
+
+/// <summary>
+/// Implementation of PDF attachment client.
+/// </summary>
+public class PdfAttachmentClient(HttpClient httpClient, ILogger<PdfAttachmentClient> logger)
+    : BaseDocumentClient(httpClient, logger), IPdfAttachmentClient
+{
+    /// <inheritdoc />
+    public async Task<AttachmentCheckResult> CheckAttachmentsAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    {
+        Logger.LogDebug("Checking PDF attachments from stream (multipart)");
+
+        var result = await SendMultipartAsync<AttachmentCheckResult>(
+            "/api/pdf/attachments/check",
+            pdfStream,
+            "document.pdf",
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<AttachmentCheckResult> CheckAttachmentsAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    {
+        Logger.LogDebug("Checking PDF attachments from byte array (Base64 JSON)");
+
+        var request = new CheckPdfAttachmentsRequest { Base64Pdf = ToBase64(pdfBytes) };
+
+        var result = await SendJsonAsync<CheckPdfAttachmentsRequest, AttachmentCheckResult>(
+            "/api/pdf/attachments/check",
+            request,
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<Dictionary<string, Stream>> ExtractAttachmentsAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    {
+        Logger.LogDebug("Extracting PDF attachments from stream (multipart)");
+
+        var zipStream = await SendMultipartForStreamAsync(
+            "/api/pdf/attachments/extract",
+            pdfStream,
+            "document.pdf",
+            cancellationToken);
+
+        return UnzipToStreams(zipStream);
+    }
+
+    /// <inheritdoc />
+    public async Task<Dictionary<string, Stream>> ExtractAttachmentsAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    {
+        Logger.LogDebug("Extracting PDF attachments from byte array (Base64 JSON)");
+
+        var request = new ExtractPdfAttachmentsRequest { Base64Pdf = ToBase64(pdfBytes) };
+
+        var zipStream = await SendJsonForStreamAsync(
+            "/api/pdf/attachments/extract",
+            request,
+            cancellationToken);
+
+        return UnzipToStreams(zipStream);
+    }
+
+    /// <inheritdoc />
+    [Obsolete("API endpoint not implemented yet")]
+    public Task<Stream> AddAttachmentsAsync(Stream pdfStream, List<AttachmentRequestDto> attachments, CancellationToken cancellationToken = default)
+    {
+        Logger.LogWarning("AddAttachments endpoint is not implemented yet in API");
+        throw new NotImplementedException("API endpoint /api/pdf/attachments/add is not implemented yet");
+    }
+
+    /// <inheritdoc />
+    [Obsolete("API endpoint not implemented yet")]
+    public Task<Stream> AddAttachmentsAsync(byte[] pdfBytes, List<AttachmentRequestDto> attachments, CancellationToken cancellationToken = default)
+    {
+        Logger.LogWarning("AddAttachments endpoint is not implemented yet in API");
+        throw new NotImplementedException("API endpoint /api/pdf/attachments/add is not implemented yet");
+    }
+
+    // ?????????????????????????????????????????????????????????????????????????
+    // Private helpers
+    // ?????????????????????????????????????????????????????????????????????????
+
+    /// <summary>
+    /// Reads a ZIP stream and returns a dictionary mapping each entry's full name
+    /// to an in-memory <see cref="MemoryStream"/> containing the decompressed bytes.
+    /// The caller owns the returned streams and is responsible for disposing them.
+    /// </summary>
+    private static Dictionary<string, Stream> UnzipToStreams(Stream zipStream)
+    {
+        var result = new Dictionary<string, Stream>(StringComparer.OrdinalIgnoreCase);
+
+        using var archive = new ZipArchive(zipStream, ZipArchiveMode.Read, leaveOpen: false);
+
+        foreach (var entry in archive.Entries)
+        {
+            // Skip directory entries (name ends with '/')
+            if (string.IsNullOrEmpty(entry.Name))
+                continue;
+
+            var ms = new MemoryStream((int)entry.Length);
+
+            using (var entryStream = entry.Open())
+            {
+                entryStream.CopyTo(ms);
+            }
+
+            ms.Position = 0;
+            result[entry.FullName] = ms;
+        }
+
+        return result;
+    }
+}
+
diff --git a/DocumentService.Client/Clients/PdfConversionClient.cs b/DocumentService.Client/Clients/PdfConversionClient.cs
new file mode 100644
index 0000000..0ecb0ed
--- /dev/null
+++ b/DocumentService.Client/Clients/PdfConversionClient.cs
@@ -0,0 +1,48 @@
+using DocumentService.Client.Interfaces;
+using DocumentService.Client.Models.Requests;
+using Microsoft.Extensions.Logging;
+using System.Net.Http;
+
+namespace DocumentService.Client.Clients;
+
+/// <summary>
+/// Implementation of PDF conversion client (PDF ? PDF/A).
+/// </summary>
+/// <remarks>
+/// All methods throw <see cref="NotImplementedException"/> because the corresponding
+/// API endpoints are not yet implemented on the server side.
+/// </remarks>
+public class PdfConversionClient(HttpClient httpClient, ILogger<PdfConversionClient> logger) : BaseDocumentClient(httpClient, logger), IPdfConversionClient
+{
+    /// <inheritdoc />
+    [Obsolete("API endpoint not implemented yet")]
+    public Task<Stream> ConvertToPdfAAsync(Stream pdfStream, string pdfALevel = "PDF/A-3b", CancellationToken cancellationToken = default)
+    {
+        Logger.LogWarning("ConvertToPdfA endpoint is not implemented yet in API");
+        throw new NotImplementedException("API endpoint POST /api/pdf/conversion/to-pdfa is not implemented yet");
+    }
+
+    /// <inheritdoc />
+    [Obsolete("API endpoint not implemented yet")]
+    public Task<Stream> ConvertToPdfAAsync(byte[] pdfBytes, string pdfALevel = "PDF/A-3b", CancellationToken cancellationToken = default)
+    {
+        Logger.LogWarning("ConvertToPdfA endpoint is not implemented yet in API");
+        throw new NotImplementedException("API endpoint POST /api/pdf/conversion/to-pdfa is not implemented yet");
+    }
+
+    /// <inheritdoc />
+    [Obsolete("API endpoint not implemented yet")]
+    public Task<Stream> ConvertFromPdfAAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    {
+        Logger.LogWarning("ConvertFromPdfA endpoint is not implemented yet in API");
+        throw new NotImplementedException("API endpoint POST /api/pdf/conversion/from-pdfa is not implemented yet");
+    }
+
+    /// <inheritdoc />
+    [Obsolete("API endpoint not implemented yet")]
+    public Task<Stream> ConvertFromPdfAAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    {
+        Logger.LogWarning("ConvertFromPdfA endpoint is not implemented yet in API");
+        throw new NotImplementedException("API endpoint POST /api/pdf/conversion/from-pdfa is not implemented yet");
+    }
+}
diff --git a/DocumentService.Client/Clients/PdfOperationsClient.cs b/DocumentService.Client/Clients/PdfOperationsClient.cs
new file mode 100644
index 0000000..3ba4919
--- /dev/null
+++ b/DocumentService.Client/Clients/PdfOperationsClient.cs
@@ -0,0 +1,161 @@
+using DocumentService.Client.Interfaces;
+using DocumentService.Client.Models.Requests;
+using Microsoft.Extensions.Logging;
+using System.Net.Http;
+using System.Net.Http.Headers;
+
+namespace DocumentService.Client.Clients;
+
+/// <summary>
+/// Implementation of PDF operations client (merge, annotate, stamp).
+/// </summary>
+public class PdfOperationsClient(HttpClient httpClient, ILogger<PdfOperationsClient> logger) : BaseDocumentClient(httpClient, logger), IPdfOperationsClient
+{
+
+    // ==================== MERGE OPERATIONS ====================
+
+    /// <inheritdoc />
+    public async Task<Stream> MergeAsync(IEnumerable<Stream> pdfStreams, List<string?>? pageRanges = null, CancellationToken cancellationToken = default)
+    {
+        using var content = new MultipartFormDataContent();
+
+        foreach (var stream in pdfStreams)
+        {
+            var streamContent = new StreamContent(stream);
+            streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
+            content.Add(streamContent, "files", $"file_{Guid.NewGuid()}.pdf");
+        }
+
+        return await SendMultipartContentForStreamAsync("/api/pdf/operations/merge", content, cancellationToken);
+    }
+
+    /// <inheritdoc />
+    public async Task<Stream> MergeAsync(IEnumerable<byte[]> pdfByteArrays, List<string?>? pageRanges = null, CancellationToken cancellationToken = default)
+    {
+        var request = new MergePdfsBase64Request
+        {
+            Base64Pdfs = [.. pdfByteArrays.Select(ToBase64)],
+            PageRanges = pageRanges
+        };
+
+        return await SendJsonForStreamAsync(
+            "/api/pdf/operations/merge",
+            request,
+            cancellationToken);
+    }
+
+    // ==================== ANNOTATION OPERATIONS ====================
+
+    /// <inheritdoc />
+    public async Task<Stream> AnnotateAsync(Stream pdfStream, AddAnnotationBase64Request request, CancellationToken cancellationToken = default)
+    {
+        // For multipart, we need to send form data with all annotation parameters
+        using var content = new MultipartFormDataContent();
+        
+        var streamContent = new StreamContent(pdfStream);
+        streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
+        content.Add(streamContent, "File", "document.pdf");
+
+        // Add annotation parameters as form fields
+        content.Add(new StringContent(request.AnnotationType.ToString()), "AnnotationType");
+        content.Add(new StringContent(request.PageNumber.ToString()), "PageNumber");
+        content.Add(new StringContent(request.X1.ToString()), "X1");
+        content.Add(new StringContent(request.Y1.ToString()), "Y1");
+        
+        if (request.X2.HasValue)
+            content.Add(new StringContent(request.X2.Value.ToString()), "X2");
+        if (request.Y2.HasValue)
+            content.Add(new StringContent(request.Y2.Value.ToString()), "Y2");
+        if (request.Width.HasValue)
+            content.Add(new StringContent(request.Width.Value.ToString()), "Width");
+        if (request.Height.HasValue)
+            content.Add(new StringContent(request.Height.Value.ToString()), "Height");
+        if (!string.IsNullOrEmpty(request.Content))
+            content.Add(new StringContent(request.Content), "Content");
+        if (!string.IsNullOrEmpty(request.Author))
+            content.Add(new StringContent(request.Author), "Author");
+        if (!string.IsNullOrEmpty(request.Color))
+            content.Add(new StringContent(request.Color), "Color");
+        if (request.TextMarkupStyle.HasValue)
+            content.Add(new StringContent(request.TextMarkupStyle.Value.ToString()), "TextMarkupStyle");
+        
+        content.Add(new StringContent(request.Origin.ToString()), "Origin");
+
+        return await SendMultipartContentForStreamAsync("/api/pdf/operations/annotate", content, cancellationToken);
+    }
+
+    /// <inheritdoc />
+    public async Task<Stream> AnnotateAsync(byte[] pdfBytes, AddAnnotationBase64Request request, CancellationToken cancellationToken = default)
+    {
+        var requestWithPdf = request with { Base64Pdf = ToBase64(pdfBytes) };
+
+        return await SendJsonForStreamAsync(
+            "/api/pdf/operations/annotate",
+            requestWithPdf,
+            cancellationToken);
+    }
+
+    // ==================== STAMP OPERATIONS ====================
+
+    /// <inheritdoc />
+    public async Task<Stream> StampAsync(Stream pdfStream, AddStampBase64Request request, CancellationToken cancellationToken = default)
+    {
+        // For multipart, we need to send form data with all stamp parameters
+        using var content = new MultipartFormDataContent();
+        
+        var streamContent = new StreamContent(pdfStream);
+        streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
+        content.Add(streamContent, "File", "document.pdf");
+
+        // Add stamp parameters as form fields
+        content.Add(new StringContent(request.StampType.ToString()), "StampType");
+        content.Add(new StringContent(request.X.ToString()), "X");
+        content.Add(new StringContent(request.Y.ToString()), "Y");
+        
+        if (request.PageNumbers != null && request.PageNumbers.Length > 0)
+        {
+            foreach (var pageNum in request.PageNumbers)
+            {
+                content.Add(new StringContent(pageNum.ToString()), "PageNumbers");
+            }
+        }
+
+        if (request.Width.HasValue)
+            content.Add(new StringContent(request.Width.Value.ToString()), "Width");
+        if (request.Height.HasValue)
+            content.Add(new StringContent(request.Height.Value.ToString()), "Height");
+        
+        content.Add(new StringContent(request.Origin.ToString()), "Origin");
+        
+        if (!string.IsNullOrEmpty(request.Text))
+            content.Add(new StringContent(request.Text), "Text");
+        if (!string.IsNullOrEmpty(request.FontName))
+            content.Add(new StringContent(request.FontName), "FontName");
+        if (request.FontSize.HasValue)
+            content.Add(new StringContent(request.FontSize.Value.ToString()), "FontSize");
+        if (!string.IsNullOrEmpty(request.Color))
+            content.Add(new StringContent(request.Color), "Color");
+        if (request.Opacity.HasValue)
+            content.Add(new StringContent(request.Opacity.Value.ToString()), "Opacity");
+        if (request.Rotation.HasValue)
+            content.Add(new StringContent(request.Rotation.Value.ToString()), "Rotation");
+        
+        content.Add(new StringContent(request.Placement.ToString()), "Placement");
+        
+        if (request.PredefinedType.HasValue)
+            content.Add(new StringContent(request.PredefinedType.Value.ToString()), "PredefinedType");
+
+        return await SendMultipartContentForStreamAsync("/api/pdf/operations/stamp", content, cancellationToken);
+    }
+
+    /// <inheritdoc />
+    public async Task<Stream> StampAsync(byte[] pdfBytes, AddStampBase64Request request, CancellationToken cancellationToken = default)
+    {
+        var requestWithPdf = request with { Base64Pdf = ToBase64(pdfBytes) };
+
+        return await SendJsonForStreamAsync(
+            "/api/pdf/operations/stamp",
+            requestWithPdf,
+            cancellationToken);
+    }
+}
diff --git a/DocumentService.Client/Clients/PdfValidationClient.cs b/DocumentService.Client/Clients/PdfValidationClient.cs
new file mode 100644
index 0000000..bb2a179
--- /dev/null
+++ b/DocumentService.Client/Clients/PdfValidationClient.cs
@@ -0,0 +1,68 @@
+using DocumentService.Client.Interfaces;
+using DocumentService.Client.Models.Requests;
+using Microsoft.Extensions.Logging;
+using System.Net.Http;
+
+namespace DocumentService.Client.Clients;
+
+/// <summary>
+/// Implementation of PDF validation client.
+/// </summary>
+public class PdfValidationClient(HttpClient httpClient, ILogger<PdfValidationClient> logger) : BaseDocumentClient(httpClient, logger), IPdfValidationClient
+{
+    /// <inheritdoc />
+    public async Task<PdfValidationResult> ValidatePdfAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    {
+        var result = await SendMultipartAsync<PdfValidationResult>(
+            "/api/pdf/validation/validate",
+            pdfStream,
+            "document.pdf",
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<PdfValidationResult> ValidatePdfAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    {
+        var request = new ValidatePdfBase64Request
+        {
+            Base64Pdf = ToBase64(pdfBytes)
+        };
+
+        var result = await SendJsonAsync<ValidatePdfBase64Request, PdfValidationResult>(
+            "/api/pdf/validation/validate",
+            request,
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<PdfAValidationResult> ValidatePdfAAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    {
+        var result = await SendMultipartAsync<PdfAValidationResult>(
+            "/api/pdf/validation/validate-pdfa",
+            pdfStream,
+            "document.pdf",
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<PdfAValidationResult> ValidatePdfAAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    {
+        var request = new ValidatePdfABase64Request
+        {
+            Base64Pdf = ToBase64(pdfBytes)
+        };
+
+        var result = await SendJsonAsync<ValidatePdfABase64Request, PdfAValidationResult>(
+            "/api/pdf/validation/validate-pdfa",
+            request,
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+}
diff --git a/DocumentService.Client/Clients/SwissQrCodeClient.cs b/DocumentService.Client/Clients/SwissQrCodeClient.cs
new file mode 100644
index 0000000..ada933d
--- /dev/null
+++ b/DocumentService.Client/Clients/SwissQrCodeClient.cs
@@ -0,0 +1,44 @@
+using DocumentService.Client.Interfaces;
+using DocumentService.Client.Models.Requests;
+using Microsoft.Extensions.Logging;
+using System.Net.Http;
+
+namespace DocumentService.Client.Clients;
+
+/// <summary>
+/// Implementation of Swiss QR Code extraction client.
+/// </summary>
+public class SwissQrCodeClient(HttpClient httpClient, ILogger<SwissQrCodeClient> logger) : BaseDocumentClient(httpClient, logger), ISwissQrCodeClient
+{
+    /// <inheritdoc />
+    public async Task<SwissQrCodeExtractionResult> ExtractSwissQrCodeAsync(Stream pdfStream, bool raw = false, CancellationToken cancellationToken = default)
+    {
+        var endpoint = $"/api/pdf/qr-code/extract-swiss?raw={raw}";
+
+        var result = await SendMultipartAsync<SwissQrCodeExtractionResult>(
+            endpoint,
+            pdfStream,
+            "document.pdf",
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<SwissQrCodeExtractionResult> ExtractSwissQrCodeAsync(byte[] pdfBytes, bool raw = false, CancellationToken cancellationToken = default)
+    {
+        var endpoint = $"/api/pdf/qr-code/extract-swiss?raw={raw}";
+
+        var request = new ExtractSwissQrCodeBase64Request
+        {
+            Base64Pdf = ToBase64(pdfBytes)
+        };
+
+        var result = await SendJsonAsync<ExtractSwissQrCodeBase64Request, SwissQrCodeExtractionResult>(
+            endpoint,
+            request,
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+}
diff --git a/DocumentService.Client/Clients/ZugferdClient.cs b/DocumentService.Client/Clients/ZugferdClient.cs
new file mode 100644
index 0000000..b7f1589
--- /dev/null
+++ b/DocumentService.Client/Clients/ZugferdClient.cs
@@ -0,0 +1,87 @@
+using DocumentService.Client.Interfaces;
+using DocumentService.Client.Models.Requests;
+using Microsoft.Extensions.Logging;
+using System.Net.Http;
+
+namespace DocumentService.Client.Clients;
+
+/// <summary>
+/// Implementation of ZUGFeRD client (detection and extraction).
+/// </summary>
+public class ZugferdClient(HttpClient httpClient, ILogger<ZugferdClient> logger) : BaseDocumentClient(httpClient, logger), IZugferdClient
+{
+    /// <inheritdoc />
+    public async Task<ZugferdCheckResult> HasZugferdAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    {
+        var result = await SendMultipartAsync<ZugferdCheckResult>(
+            "/api/pdf/zugferd/has-zugferd",
+            pdfStream,
+            "document.pdf",
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<ZugferdCheckResult> HasZugferdAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    {
+        var request = new HasZugferdRequest { Base64Pdf = ToBase64(pdfBytes) };
+
+        var result = await SendJsonAsync<HasZugferdRequest, ZugferdCheckResult>(
+            "/api/pdf/zugferd/has-zugferd",
+            request,
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<Stream> ExtractZugferdAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    {
+        // asFile=true returns the XML file directly (application/xml stream)
+        return await SendMultipartForStreamAsync(
+            "/api/pdf/zugferd/extract?asFile=true",
+            pdfStream,
+            "document.pdf",
+            cancellationToken);
+    }
+
+    /// <inheritdoc />
+    public async Task<Stream> ExtractZugferdAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    {
+        var request = new ExtractZugferdRequest { Base64Pdf = ToBase64(pdfBytes) };
+
+        // format=file returns the XML file directly (application/xml stream)
+        return await SendJsonForStreamAsync(
+            "/api/pdf/zugferd/extract?format=file",
+            request,
+            cancellationToken);
+    }
+
+    /// <inheritdoc />
+    public async Task<ZugferdExtractionResult> ExtractZugferdAsResultAsync(Stream pdfStream, CancellationToken cancellationToken = default)
+    {
+        // asFile=false returns JSON with metadata + XML content
+        var result = await SendMultipartAsync<ZugferdExtractionResult>(
+            "/api/pdf/zugferd/extract?asFile=false",
+            pdfStream,
+            "document.pdf",
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+
+    /// <inheritdoc />
+    public async Task<ZugferdExtractionResult> ExtractZugferdAsResultAsync(byte[] pdfBytes, CancellationToken cancellationToken = default)
+    {
+        var request = new ExtractZugferdRequest { Base64Pdf = ToBase64(pdfBytes) };
+
+        // format=json returns JSON with metadata + XML content
+        var result = await SendJsonAsync<ExtractZugferdRequest, ZugferdExtractionResult>(
+            "/api/pdf/zugferd/extract?format=json",
+            request,
+            cancellationToken);
+
+        return result ?? throw new InvalidOperationException("API returned null response");
+    }
+}