Add interfaces and DTOs for PDF operations support

Introduced multiple interfaces and DTOs to support a wide range of
PDF-related operations, including attachment handling, conversion,
validation, annotation, stamping, and metadata extraction.

Key changes:
- Added `DocumentServiceClientOptions` for HTTP client config.
- Introduced `IPdfAttachmentClient` for attachment operations.
- Added `IPdfConversionClient` for PDF/A conversion (marked obsolete).
- Added `IPdfOperationsClient` for merge, annotate, and stamp ops.
- Introduced `IPdfValidationClient` for PDF and PDF/A validation.
- Added `ISwissQrCodeClient` for Swiss QR Code extraction.
- Added `IZugferdClient` for ZUGFeRD detection and extraction.
- Created request DTOs for Base64-encoded operations.
- Added enums for annotation, stamp, and validation configurations.

These changes provide a flexible and extensible foundation for
interacting with PDF documents, supporting both multipart and
Base64-encoded inputs, and ensuring type safety with enums and records.

DocumentService.Client/Models/Requests/PdfAttachmentRequests.cs

@@ -0,0 +1,66 @@
+namespace DocumentService.Client.Models.Requests;
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF attachment check
+/// </summary>
+public record CheckPdfAttachmentsRequest
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+}
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF attachment extraction
+/// </summary>
+public record ExtractPdfAttachmentsRequest
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+}
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF with attachments to add
+/// </summary>
+public record AddAttachmentsRequest
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+
+    /// <summary>
+    /// List of attachments to embed
+    /// </summary>
+    public required List<AttachmentRequestDto> Attachments { get; init; }
+}
+
+/// <summary>
+/// DTO for attachment file in request
+/// </summary>
+public record AttachmentRequestDto
+{
+    /// <summary>
+    /// File name (e.g., "invoice.xml", "document.pdf")
+    /// </summary>
+    /// <example>factur-x.xml</example>
+    public required string FileName { get; init; }
+
+    /// <summary>
+    /// File content encoded as Base64 string
+    /// </summary>
+    /// <example>PD94bWwgdmVyc2lvbj0iMS4wIj8+...</example>
+    public required string Base64Content { get; init; }
+
+    /// <summary>
+    /// MIME type (optional, e.g., "application/xml")
+    /// </summary>
+    /// <example>application/xml</example>
+    public string? MimeType { get; init; }
+}

DocumentService.Client/Models/Requests/PdfConversionRequests.cs

@@ -0,0 +1,31 @@
+namespace DocumentService.Client.Models.Requests;
+
+/// <summary>
+/// Request DTO for converting a standard PDF to PDF/A format (Base64 JSON)
+/// </summary>
+public record ConvertToPdfARequest
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+
+    /// <summary>
+    /// Target PDF/A conformance level. Defaults to "PDF/A-3b".
+    /// </summary>
+    /// <example>PDF/A-3b</example>
+    public string? PdfALevel { get; init; }
+}
+
+/// <summary>
+/// Request DTO for converting a PDF/A document back to standard PDF (Base64 JSON)
+/// </summary>
+public record ConvertFromPdfARequest
+{
+    /// <summary>
+    /// PDF/A document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+}

DocumentService.Client/Models/Requests/PdfOperationRequests.cs

@@ -0,0 +1,221 @@
+using DocumentService.Client.Models.ValueObjects;
+
+namespace DocumentService.Client.Models.Requests;
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF merge operation
+/// </summary>
+public record MergePdfsBase64Request
+{
+    /// <summary>
+    /// Array of Base64-encoded PDF files (minimum 2 required)
+    /// </summary>
+    /// <example>["JVBERi0xLjQK...", "JVBERi0xLjQK..."]</example>
+    public required List<string> Base64Pdfs { get; init; }
+
+    /// <summary>
+    /// Optional page ranges per PDF (null = all pages). 
+    /// Format: "1-3,5" means pages 1, 2, 3, and 5.
+    /// If provided, array length must match Base64Pdfs length.
+    /// </summary>
+    /// <example>["1-2", "1,3,5", null]</example>
+    public List<string?>? PageRanges { get; init; }
+}
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF annotation
+/// </summary>
+public record AddAnnotationBase64Request
+{
+    /// <summary>
+    /// Base64-encoded PDF file
+    /// </summary>
+    /// <example>"JVBERi0xLjQK..."</example>
+    public required string Base64Pdf { get; init; }
+
+    /// <summary>
+    /// Type of annotation to add
+    /// </summary>
+    /// <example>TextMarkup</example>
+    public required AnnotationType AnnotationType { get; init; }
+
+    /// <summary>
+    /// Target page number (1-indexed)
+    /// </summary>
+    /// <example>1</example>
+    public required int PageNumber { get; init; }
+
+    /// <summary>
+    /// Rectangle X1 coordinate (left)
+    /// </summary>
+    /// <example>100.0</example>
+    public required double X1 { get; init; }
+
+    /// <summary>
+    /// Rectangle Y1 coordinate (top or bottom depending on Origin)
+    /// </summary>
+    /// <example>100.0</example>
+    public required double Y1 { get; init; }
+
+    /// <summary>
+    /// Rectangle X2 coordinate (right). Optional if Width is provided.
+    /// </summary>
+    /// <example>200.0</example>
+    public double? X2 { get; init; }
+
+    /// <summary>
+    /// Rectangle Y2 coordinate (bottom or top depending on Origin). Optional if Height is provided.
+    /// </summary>
+    /// <example>120.0</example>
+    public double? Y2 { get; init; }
+
+    /// <summary>
+    /// Rectangle width. Alternative to X2 (X2 = X1 + Width). Optional if X2 is provided.
+    /// </summary>
+    /// <example>100.0</example>
+    public double? Width { get; init; }
+
+    /// <summary>
+    /// Rectangle height. Alternative to Y2 (Y2 = Y1 + Height). Optional if Y2 is provided.
+    /// </summary>
+    /// <example>20.0</example>
+    public double? Height { get; init; }
+
+    /// <summary>
+    /// Annotation content (required for FreeText and StickyNote)
+    /// </summary>
+    /// <example>"Important text to highlight"</example>
+    public string? Content { get; init; }
+
+    /// <summary>
+    /// Author name (optional)
+    /// </summary>
+    /// <example>"John Doe"</example>
+    public string? Author { get; init; }
+
+    /// <summary>
+    /// Hex color (6 digits, e.g., "FF0000" for red). Optional - defaults vary by annotation type.
+    /// </summary>
+    /// <example>"FFFF00"</example>
+    public string? Color { get; init; }
+
+    /// <summary>
+    /// Text markup style (Highlight, Underline, or Strikeout). Required for TextMarkup annotations.
+    /// </summary>
+    /// <example>Highlight</example>
+    public TextMarkupStyle? TextMarkupStyle { get; init; }
+
+    /// <summary>
+    /// Coordinate origin (BottomLeft = PDF native, TopLeft = UI-friendly). Default: BottomLeft
+    /// </summary>
+    /// <example>BottomLeft</example>
+    public AnnotationOrigin Origin { get; init; } = AnnotationOrigin.BottomLeft;
+}
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF stamp operation
+/// </summary>
+public record AddStampBase64Request
+{
+    /// <summary>
+    /// Base64-encoded PDF file
+    /// </summary>
+    /// <example>"JVBERi0xLjQK..."</example>
+    public required string Base64Pdf { get; init; }
+
+    /// <summary>
+    /// Type of stamp (Text, Image, or Predefined)
+    /// </summary>
+    /// <example>Text</example>
+    public required StampType StampType { get; init; }
+
+    /// <summary>
+    /// Target page numbers (1-indexed). Null or empty = all pages.
+    /// </summary>
+    /// <example>[1, 3, 5]</example>
+    public int[]? PageNumbers { get; init; }
+
+    /// <summary>
+    /// Stamp position X coordinate
+    /// </summary>
+    /// <example>100.0</example>
+    public required double X { get; init; }
+
+    /// <summary>
+    /// Stamp position Y coordinate
+    /// </summary>
+    /// <example>100.0</example>
+    public required double Y { get; init; }
+
+    /// <summary>
+    /// Stamp width (optional, auto-size for images if not specified)
+    /// </summary>
+    /// <example>200.0</example>
+    public double? Width { get; init; }
+
+    /// <summary>
+    /// Stamp height (optional, auto-size for images if not specified)
+    /// </summary>
+    /// <example>50.0</example>
+    public double? Height { get; init; }
+
+    /// <summary>
+    /// Coordinate origin (BottomLeft = PDF native, TopLeft = UI-friendly). Default: BottomLeft
+    /// </summary>
+    /// <example>BottomLeft</example>
+    public AnnotationOrigin Origin { get; init; } = AnnotationOrigin.BottomLeft;
+
+    /// <summary>
+    /// Text content (required for Text stamps)
+    /// </summary>
+    /// <example>"CONFIDENTIAL"</example>
+    public string? Text { get; init; }
+
+    /// <summary>
+    /// Font name (default: Arial)
+    /// </summary>
+    /// <example>"Arial"</example>
+    public string? FontName { get; init; }
+
+    /// <summary>
+    /// Font size in points (default: 12)
+    /// </summary>
+    /// <example>24.0</example>
+    public double? FontSize { get; init; }
+
+    /// <summary>
+    /// Hex color (6 digits, e.g., "FF0000" for red, default: "000000")
+    /// </summary>
+    /// <example>"FF0000"</example>
+    public string? Color { get; init; }
+
+    /// <summary>
+    /// Opacity (0.0 = transparent, 1.0 = opaque, default: 0.5)
+    /// </summary>
+    /// <example>0.5</example>
+    public double? Opacity { get; init; }
+
+    /// <summary>
+    /// Rotation angle in degrees (0-360, default: 0)
+    /// </summary>
+    /// <example>45.0</example>
+    public double? Rotation { get; init; }
+
+    /// <summary>
+    /// Stamp placement (Foreground = on top, Background = watermark effect, default: Foreground)
+    /// </summary>
+    /// <example>Foreground</example>
+    public StampPlacement Placement { get; init; } = StampPlacement.Foreground;
+
+    /// <summary>
+    /// Base64-encoded image (required for Image stamps, PNG/JPEG)
+    /// </summary>
+    /// <example>"iVBORw0KGgoAAAANSUhEUgAA..."</example>
+    public string? Base64Image { get; init; }
+
+    /// <summary>
+    /// Predefined stamp type (required for Predefined stamps)
+    /// </summary>
+    /// <example>Confidential</example>
+    public PredefinedStampType? PredefinedType { get; init; }
+}

DocumentService.Client/Models/Requests/PdfValidationRequests.cs

@@ -0,0 +1,27 @@
+using DocumentService.Client.Models.ValueObjects;
+
+namespace DocumentService.Client.Models.Requests;
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF validation
+/// </summary>
+public record ValidatePdfBase64Request
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+}
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF/A validation
+/// </summary>
+public record ValidatePdfABase64Request
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+}

DocumentService.Client/Models/Requests/SwissQrCodeRequests.cs

@@ -0,0 +1,13 @@
+namespace DocumentService.Client.Models.Requests;
+
+/// <summary>
+/// Request DTO for Base64-encoded Swiss QR Code extraction
+/// </summary>
+public record ExtractSwissQrCodeBase64Request
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+}

DocumentService.Client/Models/Requests/ZugferdRequests.cs

@@ -0,0 +1,25 @@
+namespace DocumentService.Client.Models.Requests;
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF ZUGFeRD check
+/// </summary>
+public record HasZugferdRequest
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+}
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF ZUGFeRD extraction
+/// </summary>
+public record ExtractZugferdRequest
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public required string Base64Pdf { get; init; }
+}

DocumentService.Client/Models/ValueObjects/AnnotationOrigin.cs

@@ -0,0 +1,17 @@
+namespace DocumentService.Client.Models.ValueObjects;
+
+/// <summary>
+/// Coordinate origin point for PDF annotations.
+/// </summary>
+public enum AnnotationOrigin
+{
+    /// <summary>
+    /// Bottom-left corner (PDF native coordinate system, default)
+    /// </summary>
+    BottomLeft,
+    
+    /// <summary>
+    /// Top-left corner (common in UI frameworks)
+    /// </summary>
+    TopLeft
+}

DocumentService.Client/Models/ValueObjects/AnnotationType.cs

@@ -0,0 +1,32 @@
+namespace DocumentService.Client.Models.ValueObjects;
+
+/// <summary>
+/// Supported PDF annotation types
+/// </summary>
+public enum AnnotationType
+{
+    /// <summary>
+    /// Text markup annotation (highlight, underline, strikeout)
+    /// </summary>
+    TextMarkup,
+    
+    /// <summary>
+    /// Free text annotation (text box with visible text)
+    /// </summary>
+    FreeText,
+    
+    /// <summary>
+    /// Sticky note annotation (popup comment icon)
+    /// </summary>
+    StickyNote,
+    
+    /// <summary>
+    /// Circle shape annotation
+    /// </summary>
+    Circle,
+    
+    /// <summary>
+    /// Square shape annotation
+    /// </summary>
+    Square
+}

DocumentService.Client/Models/ValueObjects/OnReconfigure.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace DocumentService.Client.Models.ValueObjects;
+
+public enum OnReconfigure
+{
+    ThrowException = 0,
+    Ignore = 1,
+}

DocumentService.Client/Models/ValueObjects/PredefinedStampType.cs

@@ -0,0 +1,32 @@
+namespace DocumentService.Client.Models.ValueObjects;
+
+/// <summary>
+/// Predefined stamp types with standard text and styling.
+/// </summary>
+public enum PredefinedStampType
+{
+    /// <summary>
+    /// CONFIDENTIAL stamp (red, bold).
+    /// </summary>
+    Confidential,
+
+    /// <summary>
+    /// APPROVED stamp (green, bold).
+    /// </summary>
+    Approved,
+
+    /// <summary>
+    /// DRAFT stamp (gray, italic).
+    /// </summary>
+    Draft,
+
+    /// <summary>
+    /// VOID stamp (red, strikethrough effect).
+    /// </summary>
+    Void,
+
+    /// <summary>
+    /// FOR REVIEW stamp (orange, bold).
+    /// </summary>
+    ForReview
+}

DocumentService.Client/Models/ValueObjects/StampPlacement.cs

@@ -0,0 +1,17 @@
+namespace DocumentService.Client.Models.ValueObjects;
+
+/// <summary>
+/// Specifies whether the stamp should appear in the foreground or background.
+/// </summary>
+public enum StampPlacement
+{
+    /// <summary>
+    /// Stamp appears on top of existing page content.
+    /// </summary>
+    Foreground,
+
+    /// <summary>
+    /// Stamp appears behind existing page content (watermark effect).
+    /// </summary>
+    Background
+}

DocumentService.Client/Models/ValueObjects/StampType.cs

@@ -0,0 +1,22 @@
+namespace DocumentService.Client.Models.ValueObjects;
+
+/// <summary>
+/// Specifies the type of stamp to add to a PDF document.
+/// </summary>
+public enum StampType
+{
+    /// <summary>
+    /// Text-based stamp with custom text, font, and color.
+    /// </summary>
+    Text,
+
+    /// <summary>
+    /// Image-based stamp (PNG/JPEG overlay).
+    /// </summary>
+    Image,
+
+    /// <summary>
+    /// Predefined stamp with standard text (e.g., CONFIDENTIAL, APPROVED).
+    /// </summary>
+    Predefined
+}

DocumentService.Client/Models/ValueObjects/TextMarkupStyle.cs

@@ -0,0 +1,22 @@
+namespace DocumentService.Client.Models.ValueObjects;
+
+/// <summary>
+/// Text markup annotation style (highlight, underline, strikeout)
+/// </summary>
+public enum TextMarkupStyle
+{
+    /// <summary>
+    /// Highlight text with background color
+    /// </summary>
+    Highlight,
+    
+    /// <summary>
+    /// Underline text
+    /// </summary>
+    Underline,
+    
+    /// <summary>
+    /// Strikeout text (strikethrough)
+    /// </summary>
+    Strikeout
+}