feat(Extensions): Add PDF editing extension methods using iText

- Introduced `Edit` extension methods for `Stream` and `byte[]` to allow
  in-place PDF modifications via a `PdfDocument` action.
- Supports both .NET and .NET Framework projects.
- Ensures proper disposal of streams and PdfDocument instances.

EnvelopeGenerator.PdfEditor/Extensions.cs

@@ -0,0 +1,42 @@
+using iText.Kernel.Colors;
+using iText.Kernel.Pdf;
+using iText.Kernel.Pdf.Canvas;
+
+#if NETFRAMEWORK
+using System.IO;
+using System;
+#endif
+
+namespace EnvelopeGenerator.PdfEditor
+#if NET
+    ;
+#elif NETFRAMEWORK
+{
+#endif
+
+    public static class Extensions
+    {
+        public static TStream Edit<TStream>(this TStream inputStream, Action<PdfDocument> edit)
+            where TStream : Stream, new()
+        {
+            using (var outputStream = new TStream())
+            {
+                using (var pdfDoc = new PdfDocument(new PdfReader(inputStream), new PdfWriter(outputStream)))
+                {
+                    edit(pdfDoc);
+                }
+                return outputStream;
+            }
+        }
+
+        public static byte[] Edit(this byte[] pdfBytes, Action<PdfDocument> edit)
+        {
+            using (var inputStream = new MemoryStream(pdfBytes))
+            {
+                return inputStream.Edit(edit).ToArray();
+            }
+        }
+    }
+#if NETFRAMEWORK
+}
+#endif

EnvelopeGenerator.Web/Controllers/EnvelopeController.cs

@@ -1,9 +1,17 @@
 using DigitalData.Core.Abstraction.Application.DTO;
 using DigitalData.Core.API;
+using EnvelopeGenerator.Application.Common.Dto;
+using EnvelopeGenerator.Application.Common.Dto.EnvelopeReceiver;
+using EnvelopeGenerator.Application.Common.Extensions;
+using EnvelopeGenerator.Application.Common.Interfaces.Services;
 using EnvelopeGenerator.Application.EnvelopeReceivers.Queries;
 using EnvelopeGenerator.Application.Resources;
+using EnvelopeGenerator.Domain.Constants;
+using EnvelopeGenerator.PdfEditor;
 using EnvelopeGenerator.Web.Extensions;
 using EnvelopeGenerator.Web.Models;
+using iText.Kernel.Colors;
+using iText.Kernel.Pdf.Canvas;
 using MediatR;
 using Microsoft.AspNetCore.Authentication;
 using Microsoft.AspNetCore.Authentication.Cookies;
@@ -11,11 +19,6 @@ using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Localization;
 using Newtonsoft.Json;
 using OtpNet;
-using EnvelopeGenerator.Domain.Constants;
-using EnvelopeGenerator.Application.Common.Dto;
-using EnvelopeGenerator.Application.Common.Dto.EnvelopeReceiver;
-using EnvelopeGenerator.Application.Common.Extensions;
-using EnvelopeGenerator.Application.Common.Interfaces.Services;
 
 namespace EnvelopeGenerator.Web.Controllers;
 
@@ -221,6 +224,18 @@ public class EnvelopeController : ViewControllerBase
     {
         if (er.Envelope!.Documents?.FirstOrDefault() is DocumentDto doc && doc.ByteData is not null)
         {
+            doc.ByteData = doc.ByteData.Edit(doc =>
+            {
+                var page = doc.GetFirstPage();
+                var canvas = new PdfCanvas(page);
+                canvas.SetStrokeColor(ColorConstants.RED);
+                canvas.SetFillColor(ColorConstants.CYAN);
+                canvas.SetFillColorRgb(222, 220, 215);
+                canvas.SetLineWidth(2);
+                canvas.Rectangle(100, 500, 200, 100);
+                canvas.FillStroke();
+            });
+
             ViewData["DocumentBytes"] = doc.ByteData;
         }
         else

EnvelopeGenerator.Web/EnvelopeGenerator.Web.csproj

@@ -2129,6 +2129,7 @@
 	<ItemGroup>
 		<ProjectReference Include="..\EnvelopeGenerator.Application\EnvelopeGenerator.Application.csproj" />
 		<ProjectReference Include="..\EnvelopeGenerator.Infrastructure\EnvelopeGenerator.Infrastructure.csproj" />
+		<ProjectReference Include="..\EnvelopeGenerator.PdfEditor\EnvelopeGenerator.PdfEditor.csproj" />
 	</ItemGroup>
 
 	<ItemGroup>