diff --git a/DocumentOperator.Tests/Integration/API/PdfAttachmentControllerTests.cs b/DocumentOperator.Tests/Integration/API/PdfAttachmentControllerTests.cs
new file mode 100644
index 0000000..9178479
--- /dev/null
+++ b/DocumentOperator.Tests/Integration/API/PdfAttachmentControllerTests.cs
@@ -0,0 +1,251 @@
+using DocumentOperator.Application.CheckPdfAttachments.Queries;
+using DocumentOperator.Application.Common.DTOs;
+using FluentAssertions;
+using Microsoft.AspNetCore.Mvc.Testing;
+using System.Net;
+using System.Net.Http.Json;
+using Xunit;
+
+namespace DocumentOperator.Tests.Integration.API;
+
+/// <summary>
+/// Integration tests for PdfAttachmentController.
+/// Tests /api/pdf/attachments/check endpoint with both multipart and Base64 input.
+/// </summary>
+public class PdfAttachmentControllerTests : IClassFixture<WebApplicationFactory<Program>>
+{
+    private readonly WebApplicationFactory<Program> _factory;
+    private readonly HttpClient _client;
+
+    public PdfAttachmentControllerTests(WebApplicationFactory<Program> factory)
+    {
+        _factory = factory;
+        _client = _factory.CreateClient();
+    }
+
+    #region Helper Methods
+
+    /// <summary>
+    /// Loads a test PDF from embedded resources.
+    /// </summary>
+    private static async Task<byte[]> LoadTestPdfAsync(string filename)
+    {
+        var assembly = typeof(PdfAttachmentControllerTests).Assembly;
+        var resourceName = $"DocumentOperator.Tests.TestData.Pdfs.{filename}";
+
+        using var stream = assembly.GetManifestResourceStream(resourceName);
+        if (stream == null)
+        {
+            throw new InvalidOperationException($"Test resource '{resourceName}' not found");
+        }
+
+        using var ms = new MemoryStream();
+        await stream.CopyToAsync(ms);
+        return ms.ToArray();
+    }
+
+    #endregion
+
+    #region Base64 JSON Tests
+
+    [Fact]
+    public async Task POST_CheckAttachments_Base64_PdfWithoutAttachments_Returns200()
+    {
+        // Arrange
+        byte[] pdfBytes = await LoadTestPdfAsync("pdfWithSwissQRCode.pdf");
+        string base64Pdf = Convert.ToBase64String(pdfBytes);
+        var request = new CheckPdfAttachmentsQuery { Base64Pdf = base64Pdf };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/attachments/check", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.OK);
+
+        var result = await response.Content.ReadFromJsonAsync<AttachmentCheckResult>();
+        result.Should().NotBeNull();
+        result!.HasAttachments.Should().BeFalse();
+        result.AttachmentCount.Should().Be(0);
+        result.Attachments.Should().BeEmpty();
+    }
+
+    [Fact]
+    public async Task POST_CheckAttachments_Base64_PdfWithMultipleAttachments_Returns200()
+    {
+        // Arrange
+        byte[] pdfBytes = await LoadTestPdfAsync("pdfWithMoreThanOneAttachment.pdf");
+        string base64Pdf = Convert.ToBase64String(pdfBytes);
+        var request = new CheckPdfAttachmentsQuery { Base64Pdf = base64Pdf };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/attachments/check", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.OK);
+
+        var result = await response.Content.ReadFromJsonAsync<AttachmentCheckResult>();
+        result.Should().NotBeNull();
+        result!.HasAttachments.Should().BeTrue();
+        result.AttachmentCount.Should().Be(6, "PDF has exactly 6 attachments");
+        result.Attachments.Should().HaveCount(6);
+
+        // Verify each attachment has required properties
+        foreach (var attachment in result.Attachments)
+        {
+            attachment.FileName.Should().NotBeNullOrEmpty();
+            attachment.MimeType.Should().NotBeNullOrEmpty();
+            attachment.Size.Should().BeGreaterThan(0);
+        }
+    }
+
+    [Fact]
+    public async Task POST_CheckAttachments_Base64_InvalidBase64_Returns400()
+    {
+        // Arrange
+        var request = new CheckPdfAttachmentsQuery { Base64Pdf = "invalid-base64!!!" };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/attachments/check", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.BadRequest);
+
+        var problemDetails = await response.Content.ReadAsStringAsync();
+        problemDetails.Should().Contain("Base64");
+    }
+
+    [Fact]
+    public async Task POST_CheckAttachments_Base64_EmptyPdf_Returns400()
+    {
+        // Arrange
+        var request = new CheckPdfAttachmentsQuery { Base64Pdf = string.Empty };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/attachments/check", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.BadRequest);
+
+        var problemDetails = await response.Content.ReadAsStringAsync();
+        problemDetails.Should().Contain("Either PdfBytes or Base64Pdf must be provided");
+    }
+
+    #endregion
+
+    #region Multipart/Form-Data Tests
+
+    [Fact]
+    public async Task POST_CheckAttachments_Multipart_PdfWithoutAttachments_Returns200()
+    {
+        // Arrange
+        byte[] pdfBytes = await LoadTestPdfAsync("pdfWithSwissQRCode.pdf");
+
+        using var content = new MultipartFormDataContent();
+        var fileContent = new ByteArrayContent(pdfBytes);
+        fileContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/pdf");
+        content.Add(fileContent, "file", "pdfWithSwissQRCode.pdf");
+
+        // Act
+        var response = await _client.PostAsync("/api/pdf/attachments/check", content);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.OK);
+
+        var result = await response.Content.ReadFromJsonAsync<AttachmentCheckResult>();
+        result.Should().NotBeNull();
+        result!.HasAttachments.Should().BeFalse();
+        result.AttachmentCount.Should().Be(0);
+        result.Attachments.Should().BeEmpty();
+    }
+
+    [Fact]
+    public async Task POST_CheckAttachments_Multipart_PdfWithMultipleAttachments_Returns200()
+    {
+        // Arrange
+        byte[] pdfBytes = await LoadTestPdfAsync("pdfWithMoreThanOneAttachment.pdf");
+
+        using var content = new MultipartFormDataContent();
+        var fileContent = new ByteArrayContent(pdfBytes);
+        fileContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/pdf");
+        content.Add(fileContent, "file", "pdfWithMoreThanOneAttachment.pdf");
+
+        // Act
+        var response = await _client.PostAsync("/api/pdf/attachments/check", content);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.OK);
+
+        var result = await response.Content.ReadFromJsonAsync<AttachmentCheckResult>();
+        result.Should().NotBeNull();
+        result!.HasAttachments.Should().BeTrue();
+        result.AttachmentCount.Should().Be(6);
+        result.Attachments.Should().HaveCount(6);
+
+        // Verify first attachment details
+        var firstAttachment = result.Attachments.First();
+        firstAttachment.FileName.Should().NotBeNullOrEmpty();
+        firstAttachment.MimeType.Should().NotBeNullOrEmpty();
+        firstAttachment.Size.Should().BeGreaterThan(0);
+    }
+
+    [Fact]
+    public async Task POST_CheckAttachments_Multipart_MissingFile_Returns400()
+    {
+        // Arrange
+        using var content = new MultipartFormDataContent(); // No file added
+
+        // Act
+        var response = await _client.PostAsync("/api/pdf/attachments/check", content);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.BadRequest);
+    }
+
+    [Fact]
+    public async Task POST_CheckAttachments_Multipart_CorruptedPdf_Returns500()
+    {
+        // Arrange
+        byte[] corruptedBytes = "This is not a valid PDF content"u8.ToArray();
+
+        using var content = new MultipartFormDataContent();
+        var fileContent = new ByteArrayContent(corruptedBytes);
+        fileContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/pdf");
+        content.Add(fileContent, "file", "corrupted.pdf");
+
+        // Act
+        var response = await _client.PostAsync("/api/pdf/attachments/check", content);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.InternalServerError);
+
+        var problemDetails = await response.Content.ReadAsStringAsync();
+        // Note: Generic error message for security reasons (doesn't expose internal details)
+        problemDetails.Should().Contain("error");
+    }
+
+    #endregion
+
+    #region Edge Cases
+
+    [Fact]
+    public async Task POST_CheckAttachments_Base64_PdfWithSwissQrCode_Returns200()
+    {
+        // Arrange
+        byte[] pdfBytes = await LoadTestPdfAsync("pdfWithSwissQRCode.pdf");
+        string base64Pdf = Convert.ToBase64String(pdfBytes);
+        var request = new CheckPdfAttachmentsQuery { Base64Pdf = base64Pdf };
+
+        // Act
+        var response = await _client.PostAsJsonAsync("/api/pdf/attachments/check", request);
+
+        // Assert
+        response.StatusCode.Should().Be(HttpStatusCode.OK);
+
+        var result = await response.Content.ReadFromJsonAsync<AttachmentCheckResult>();
+        result.Should().NotBeNull();
+        result!.HasAttachments.Should().BeFalse("Swiss QR PDF has no attachments");
+        result.AttachmentCount.Should().Be(0);
+    }
+
+    #endregion
+}
diff --git a/DocumentOperator.Tests/Unit/Application/CheckPdfAttachments/CheckPdfAttachmentsQueryHandlerTests.cs b/DocumentOperator.Tests/Unit/Application/CheckPdfAttachments/CheckPdfAttachmentsQueryHandlerTests.cs
new file mode 100644
index 0000000..5850a74
--- /dev/null
+++ b/DocumentOperator.Tests/Unit/Application/CheckPdfAttachments/CheckPdfAttachmentsQueryHandlerTests.cs
@@ -0,0 +1,123 @@
+using AutoMapper;
+using DocumentOperator.Application.CheckPdfAttachments.Queries;
+using DocumentOperator.Application.Common.DTOs;
+using DocumentOperator.Application.Common.Interfaces;
+
+using FluentAssertions;
+using Moq;
+
+namespace DocumentOperator.Tests.Unit.Application.CheckPdfAttachments;
+
+/// <summary>
+/// Unit tests for CheckPdfAttachmentsQueryHandler.
+/// Tests handler logic with mocked dependencies (IPdfProcessor, IMapper).
+/// </summary>
+public class CheckPdfAttachmentsQueryHandlerTests
+{
+    private readonly Mock<IPdfProcessor> _mockPdfProcessor;
+    private readonly Mock<IMapper> _mockMapper;
+    private readonly CheckPdfAttachmentsQueryHandler _sut;
+
+    public CheckPdfAttachmentsQueryHandlerTests()
+    {
+        _mockPdfProcessor = new Mock<IPdfProcessor>();
+        _mockMapper = new Mock<IMapper>();
+        _sut = new CheckPdfAttachmentsQueryHandler(_mockPdfProcessor.Object, _mockMapper.Object);
+    }
+
+    [Fact]
+    public async Task Handle_WithPdfBytes_CallsProcessorAndMapper()
+    {
+        // Arrange
+        byte[] pdfBytes = "fake-pdf-content"u8.ToArray();
+        var query = new CheckPdfAttachmentsQuery { PdfBytes = pdfBytes };
+
+        var domainResult = new AttachmentInfo(
+            hasAttachments: true,
+            attachmentCount: 2,
+            attachments:
+            [
+                new("invoice.xml", "text/xml", 1024),
+                new("metadata.json", "application/json", 512)
+            ]
+        );
+
+        var expectedDto = new AttachmentCheckResult
+        {
+            HasAttachments = true,
+            AttachmentCount = 2,
+            Attachments =
+            [
+                new() { FileName = "invoice.xml", MimeType = "text/xml", Size = 1024 },
+                new() { FileName = "metadata.json", MimeType = "application/json", Size = 512 }
+            ]
+        };
+
+        _mockPdfProcessor.Setup(p => p.CheckAttachmentsAsync(It.IsAny<Stream>())).ReturnsAsync(domainResult);
+        _mockMapper.Setup(m => m.Map<AttachmentCheckResult>(domainResult)).Returns(expectedDto);
+
+        // Act
+        var result = await _sut.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().BeEquivalentTo(expectedDto);
+
+        _mockPdfProcessor.Verify(p => p.CheckAttachmentsAsync(It.IsAny<Stream>()), Times.Once);
+        _mockMapper.Verify(m => m.Map<AttachmentCheckResult>(domainResult), Times.Once);
+    }
+
+    [Fact]
+    public async Task Handle_WithBase64Pdf_DecodesAndCallsProcessor()
+    {
+        // Arrange
+        byte[] pdfBytes = "fake-pdf-content"u8.ToArray();
+        string base64Pdf = Convert.ToBase64String(pdfBytes);
+        var query = new CheckPdfAttachmentsQuery { Base64Pdf = base64Pdf };
+
+        var domainResult = new AttachmentInfo(false, 0, []);
+        var expectedDto = new AttachmentCheckResult { HasAttachments = false, AttachmentCount = 0, Attachments = [] };
+
+        _mockPdfProcessor.Setup(p => p.CheckAttachmentsAsync(It.IsAny<Stream>())).ReturnsAsync(domainResult);
+        _mockMapper.Setup(m => m.Map<AttachmentCheckResult>(domainResult)).Returns(expectedDto);
+
+        // Act
+        var result = await _sut.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.HasAttachments.Should().BeFalse();
+        result.AttachmentCount.Should().Be(0);
+
+        _mockPdfProcessor.Verify(p => p.CheckAttachmentsAsync(It.IsAny<Stream>()), Times.Once);
+    }
+
+    [Fact]
+    public async Task Handle_WithEmptyAttachments_ReturnsEmptyList()
+    {
+        // Arrange
+        byte[] pdfBytes = "fake-pdf-content"u8.ToArray();
+        var query = new CheckPdfAttachmentsQuery { PdfBytes = pdfBytes };
+
+        var domainResult = new AttachmentInfo(false, 0, []);
+        var expectedDto = new AttachmentCheckResult
+        {
+            HasAttachments = false,
+            AttachmentCount = 0,
+            Attachments = []
+        };
+
+        _mockPdfProcessor.Setup(p => p.CheckAttachmentsAsync(It.IsAny<Stream>())).ReturnsAsync(domainResult);
+        _mockMapper.Setup(m => m.Map<AttachmentCheckResult>(domainResult)).Returns(expectedDto);
+
+        // Act
+        var result = await _sut.Handle(query, CancellationToken.None);
+
+        // Assert
+        result.HasAttachments.Should().BeFalse();
+        result.AttachmentCount.Should().Be(0);
+        result.Attachments.Should().BeEmpty();
+    }
+}
+
+