Refactor: Rename DocumentOperator to DocumentService

Updated project and solution files to rename and restructure
`DocumentOperator` to `DocumentService`. Modified project
references in `DocumentService.API.csproj`, `DocumentService.Application.csproj`,
and `DocumentService.Infrastructure.csproj` to reflect the new
naming convention. Updated `DocumentService.sln` to remove
old project references, add new ones, and adjust configuration
and nested project mappings accordingly. This change aligns
the project structure with the new naming convention.

DocumentService.Domain/Common/Exceptions/BadRequestException.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.Serialization;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace DocumentService.Domain.Common.Exceptions;
+
+public class BadRequestException : Exception
+{
+    public BadRequestException()
+    {
+    }
+
+    public BadRequestException(string? message) : base(message)
+    {
+    }
+
+    public BadRequestException(string? message, Exception? innerException) : base(message, innerException)
+    {
+    }
+}

DocumentService.Domain/Common/Exceptions/DomainException.cs

@@ -0,0 +1,26 @@
+namespace DocumentService.Domain.Common.Exceptions;
+
+/// <summary>
+/// Base exception for all domain-related exceptions.
+/// Caught by the Exception Handling Middleware in the API layer.
+/// </summary>
+[Obsolete("This exception is deprecated. Use more specific exceptions for domain errors.")]
+public abstract class DomainException : Exception
+{
+    /// <summary>
+    /// Error code for categorization and logging.
+    /// </summary>
+    public string ErrorCode { get; }
+
+    protected DomainException(string message, string errorCode) 
+        : base(message)
+    {
+        ErrorCode = errorCode;
+    }
+
+    protected DomainException(string message, string errorCode, Exception innerException) 
+        : base(message, innerException)
+    {
+        ErrorCode = errorCode;
+    }
+}

DocumentService.Domain/Common/Exceptions/DomainValidationException.cs

@@ -0,0 +1,29 @@
+namespace DocumentService.Domain.Common.Exceptions;
+
+/// <summary>
+/// Exception thrown when domain validation fails (e.g., invalid Value Objects).
+/// Maps to HTTP 400 Bad Request in the API layer.
+/// </summary>
+[Obsolete("This exception is deprecated. Use more specific exceptions for domain validation errors.")]
+public class DomainValidationException : DomainException
+{
+    public string PropertyName { get; }
+
+    public DomainValidationException(string message)
+        : base(message, "DOMAIN_VALIDATION_ERROR")
+    {
+        PropertyName = string.Empty;
+    }
+
+    public DomainValidationException(string propertyName, string message)
+        : base(message, "DOMAIN_VALIDATION_ERROR")
+    {
+        PropertyName = propertyName;
+    }
+
+    public DomainValidationException(string message, Exception innerException)
+        : base(message, "DOMAIN_VALIDATION_ERROR", innerException)
+    {
+        PropertyName = string.Empty;
+    }
+}

DocumentService.Domain/Common/Exceptions/NotFoundException.cs

@@ -0,0 +1,22 @@
+using System.Runtime.Serialization;
+
+namespace DocumentService.Domain.Common.Exceptions;
+
+/// <summary>
+/// Exception thrown when a requested resource is not found.
+/// Maps to HTTP 404 Not Found in the API layer.
+/// </summary>
+public class NotFoundException : Exception
+{
+    public NotFoundException()
+    {
+    }
+
+    public NotFoundException(string? message) : base(message)
+    {
+    }
+
+    public NotFoundException(string? message, Exception? innerException) : base(message, innerException)
+    {
+    }
+}

DocumentService.Domain/DocumentService.Domain.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Remove="Common\Results\**" />
+    <Compile Remove="Constants\**" />
+    <EmbeddedResource Remove="Common\Results\**" />
+    <EmbeddedResource Remove="Constants\**" />
+    <None Remove="Common\Results\**" />
+    <None Remove="Constants\**" />
+  </ItemGroup>
+
+</Project>

DocumentService.Domain/Models/ValueObjects/AnnotationOrigin.cs

@@ -0,0 +1,18 @@
+namespace DocumentService.Domain.Models.ValueObjects;
+
+/// <summary>
+/// Coordinate origin point for PDF annotations.
+/// PDF default is BottomLeft, but users may prefer TopLeft for easier UI integration.
+/// </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.Domain/Models/ValueObjects/AnnotationType.cs

@@ -0,0 +1,32 @@
+namespace DocumentService.Domain.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.Domain/Models/ValueObjects/PredefinedStampType.cs

@@ -0,0 +1,32 @@
+namespace DocumentService.Domain.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.Domain/Models/ValueObjects/StampPlacement.cs

@@ -0,0 +1,17 @@
+namespace DocumentService.Domain.Models.ValueObjects;
+
+/// <summary>
+/// Specifies whether the stamp should appear in the foreground (on top of content) or background (behind content).
+/// </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.Domain/Models/ValueObjects/StampType.cs

@@ -0,0 +1,22 @@
+namespace DocumentService.Domain.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.Domain/Models/ValueObjects/TenantId.cs

@@ -0,0 +1,41 @@
+namespace DocumentService.Domain.Models.ValueObjects;
+
+public sealed class TenantId
+{
+    public string Value { get; }
+
+    private TenantId(string value)
+    {
+        Value = value;
+    }
+
+    public static TenantId Create(string value)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+            throw new Common.Exceptions.DomainValidationException("TenantId cannot be empty.");
+
+        if (value.Length > 100)
+            throw new Common.Exceptions.DomainValidationException("TenantId cannot exceed 100 characters.");
+
+        // Normalisierung: Lowercase
+        var normalized = value.Trim().ToLowerInvariant();
+
+        return new TenantId(normalized);
+    }
+
+    public override string ToString() => Value;
+
+    // Equality
+    public override bool Equals(object? obj)
+    {
+        if (obj is not TenantId other)
+            return false;
+
+        return Value == other.Value;
+    }
+
+    public override int GetHashCode()
+    {
+        return Value.GetHashCode();
+    }
+}

DocumentService.Domain/Models/ValueObjects/TextMarkupStyle.cs

@@ -0,0 +1,23 @@
+namespace DocumentService.Domain.Models.ValueObjects;
+
+/// <summary>
+/// Text markup annotation style (highlight, underline, strikeout)
+/// Maps to DevExpress PdfTextMarkupAnnotationType
+/// </summary>
+public enum TextMarkupStyle
+{
+    /// <summary>
+    /// Highlight text with background color
+    /// </summary>
+    Highlight,
+    
+    /// <summary>
+    /// Underline text
+    /// </summary>
+    Underline,
+    
+    /// <summary>
+    /// Strikeout text (strikethrough)
+    /// </summary>
+    Strikeout
+}