diff --git a/DocumentOperator.Application/AddStamp/AddStampCommand.cs b/DocumentOperator.Application/AddStamp/AddStampCommand.cs
new file mode 100644
index 0000000..9352298
--- /dev/null
+++ b/DocumentOperator.Application/AddStamp/AddStampCommand.cs
@@ -0,0 +1,125 @@
+using FluentValidation;
+using MediatR;
+
+namespace DocumentOperator.Application.AddStamp;
+
+/// <summary>
+/// Command to add a stamp (text, image, or predefined) to PDF pages.
+/// Combines Command, Handler, and Validator in a single file (Vertical Slice pattern).
+/// </summary>
+public record AddStampCommand : IRequest<byte[]>
+{
+    public required Stream PdfStream { get; init; }
+    public required Domain.Models.ValueObjects.StampType StampType { get; init; }
+    public int[]? PageNumbers { get; init; } // null = all pages
+    public required (double X, double Y) Position { get; init; }
+    public (double Width, double Height)? Size { get; init; }
+    public Domain.Models.ValueObjects.AnnotationOrigin Origin { get; init; } = Domain.Models.ValueObjects.AnnotationOrigin.BottomLeft;
+    public string? Text { get; init; }
+    public string? FontName { get; init; }
+    public double? FontSize { get; init; }
+    public string? Color { get; init; }
+    public double? Opacity { get; init; }
+    public double? Rotation { get; init; }
+    public Domain.Models.ValueObjects.StampPlacement Placement { get; init; } = Domain.Models.ValueObjects.StampPlacement.Foreground;
+    public byte[]? ImageBytes { get; init; }
+    public Domain.Models.ValueObjects.PredefinedStampType? PredefinedType { get; init; }
+}
+
+/// <summary>
+/// Handler for AddStampCommand.
+/// </summary>
+public class AddStampHandler(Common.Interfaces.IPdfProcessor pdfProcessor) : IRequestHandler<AddStampCommand, byte[]>
+{
+    public async Task<byte[]> Handle(AddStampCommand command, CancellationToken cancellationToken)
+    {
+        return await pdfProcessor.AddStampAsync(
+            command.PdfStream,
+            command.StampType,
+            command.PageNumbers,
+            command.Position,
+            command.Size,
+            command.Origin,
+            command.Text,
+            command.FontName,
+            command.FontSize,
+            command.Color,
+            command.Opacity,
+            command.Rotation,
+            command.Placement,
+            command.ImageBytes,
+            command.PredefinedType
+        );
+    }
+}
+
+/// <summary>
+/// Validator for AddStampCommand.
+/// </summary>
+public class AddStampValidator : AbstractValidator<AddStampCommand>
+{
+    public AddStampValidator()
+    {
+        RuleFor(x => x.PdfStream)
+            .NotNull().WithMessage("PDF stream is required");
+
+        RuleFor(x => x.Position.X)
+            .GreaterThanOrEqualTo(0).WithMessage("Position X must be >= 0");
+
+        RuleFor(x => x.Position.Y)
+            .GreaterThanOrEqualTo(0).WithMessage("Position Y must be >= 0");
+
+        // Text stamp validation
+        When(x => x.StampType == Domain.Models.ValueObjects.StampType.Text, () =>
+        {
+            RuleFor(x => x.Text)
+                .NotEmpty().WithMessage("Text is required for Text stamp type");
+        });
+
+        // Image stamp validation
+        When(x => x.StampType == Domain.Models.ValueObjects.StampType.Image, () =>
+        {
+            RuleFor(x => x.ImageBytes)
+                .NotNull().WithMessage("Image bytes are required for Image stamp type")
+                .Must(bytes => bytes != null && bytes.Length > 0).WithMessage("Image bytes cannot be empty");
+        });
+
+        // Predefined stamp validation
+        When(x => x.StampType == Domain.Models.ValueObjects.StampType.Predefined, () =>
+        {
+            RuleFor(x => x.PredefinedType)
+                .NotNull().WithMessage("Predefined type is required for Predefined stamp type");
+        });
+
+        // Optional parameter validations
+        When(x => x.Opacity.HasValue, () =>
+        {
+            RuleFor(x => x.Opacity!.Value)
+                .InclusiveBetween(0.0, 1.0).WithMessage("Opacity must be between 0.0 and 1.0");
+        });
+
+        When(x => x.Rotation.HasValue, () =>
+        {
+            RuleFor(x => x.Rotation!.Value)
+                .InclusiveBetween(0.0, 360.0).WithMessage("Rotation must be between 0 and 360 degrees");
+        });
+
+        When(x => x.FontSize.HasValue, () =>
+        {
+            RuleFor(x => x.FontSize!.Value)
+                .GreaterThan(0).WithMessage("Font size must be positive");
+        });
+
+        When(x => !string.IsNullOrWhiteSpace(x.Color), () =>
+        {
+            RuleFor(x => x.Color!)
+                .Matches(@"^[0-9A-Fa-f]{6}$").WithMessage("Color must be 6-digit hex (e.g., 'FF0000')");
+        });
+
+        When(x => x.PageNumbers != null, () =>
+        {
+            RuleFor(x => x.PageNumbers!)
+                .Must(pages => pages.All(p => p > 0)).WithMessage("All page numbers must be >= 1");
+        });
+    }
+}