Support flexible coordinate systems for PDF signatures

Added enums `PdfSignatureCoordinateUnit` and `PdfSignatureCoordinateOrigin` to support defining signature coordinates in points or inches and relative to either the bottom-left or top-left corner of the page.

Updated `PdfSignatureAppearanceDto` to include `CoordinateUnit` and `CoordinateOrigin` parameters with default values. Refactored `PdfDigitalSignatureService` to use a new `BuildSignatureBounds` method for calculating signature bounds, which handles unit conversion, origin adjustments, and validation.

Introduced `GetPageHeightInPoints` to retrieve page height for top-left origin calculations. Improved signature field naming precision and added error handling for invalid dimensions and page numbers.

Included a TODO for optimizing the signature check algorithm.

EnvelopeGenerator.Application/Common/Dto/PdfSignatureAppearanceDto.cs

@@ -3,7 +3,38 @@ namespace EnvelopeGenerator.Application.Common.Dto;
 /// <summary>
 /// 
 /// </summary>
-/// <param name="ImageBytes"></param>
+public enum PdfSignatureCoordinateUnit
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    Point = 0,
+
+    /// <summary>
+    /// 
+    /// </summary>
+    Inch = 1
+}
+
+/// <summary>
+/// 
+/// </summary>
+public enum PdfSignatureCoordinateOrigin
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    BottomLeft = 0,
+
+    /// <summary>
+    /// 
+    /// </summary>
+    TopLeft = 1
+}
+
+/// <summary>
+/// 
+/// </summary>
 /// <param name="PageNumber"></param>
 /// <param name="Left"></param>
 /// <param name="Bottom"></param>
@@ -16,6 +47,8 @@ namespace EnvelopeGenerator.Application.Common.Dto;
 /// <param name="ShowLocation"></param>
 /// <param name="ShowDistinguishedName"></param>
 /// <param name="DateTimeFormat"></param>
+/// <param name="CoordinateUnit"></param>
+/// <param name="CoordinateOrigin"></param>
 public sealed record PdfSignatureAppearanceDto(
     int PageNumber,
     double Left,
@@ -28,7 +61,9 @@ public sealed record PdfSignatureAppearanceDto(
     bool ShowReason = false,
     bool ShowLocation = false,
     bool ShowDistinguishedName = false,
-    string DateTimeFormat = "dd.MM.yyyy HH:mm:ss zzz")
+    string DateTimeFormat = "dd.MM.yyyy HH:mm:ss zzz",
+    PdfSignatureCoordinateUnit CoordinateUnit = PdfSignatureCoordinateUnit.Point,
+    PdfSignatureCoordinateOrigin CoordinateOrigin = PdfSignatureCoordinateOrigin.BottomLeft)
 {
     /// <summary>
     /// 

EnvelopeGenerator.Infrastructure.Crypt/Services/PdfDigitalSignatureService.cs

@@ -43,8 +43,8 @@ public sealed class PdfDigitalSignatureService(IOptions<Pkcs11Options> options)
 
             var builder = request.Appearance is null ? new PdfDeferredSignatureBuilder(signerInfo) : new (signerInfo, new PdfSignatureFieldInfo(request.Appearance.PageNumber)
             {
-                Name = $"Sig_{DateTimeOffset.UtcNow:yyyyMMddHHmmss}",
-                SignatureBounds = new PdfRectangle(request.Appearance.Left, request.Appearance.Bottom, request.Appearance.Left + request.Appearance.Width, request.Appearance.Bottom + request.Appearance.Height)
+                Name = $"Sig_{DateTimeOffset.UtcNow:yyyyMMddHHmmssfff}",
+                SignatureBounds = BuildSignatureBounds(request.Appearance, workingInput)
             });
 
             builder.Name = request.Name;
@@ -105,6 +105,61 @@ public sealed class PdfDigitalSignatureService(IOptions<Pkcs11Options> options)
         }
     }
 
+    private static PdfRectangle BuildSignatureBounds(PdfSignatureAppearanceDto appearance, Stream inputPdf)
+    {
+        var left = appearance.Left;
+        var bottom = appearance.Bottom;
+        var width = appearance.Width;
+        var height = appearance.Height;
+
+        if (appearance.CoordinateUnit == PdfSignatureCoordinateUnit.Inch)
+        {
+            left *= 72.0;
+            bottom *= 72.0;
+            width *= 72.0;
+            height *= 72.0;
+        }
+
+        if (width <= 0 || height <= 0)
+            throw new BadRequestException("Signature appearance width and height must be greater than zero.");
+
+        if (appearance.CoordinateOrigin == PdfSignatureCoordinateOrigin.TopLeft)
+        {
+            var pageHeight = GetPageHeightInPoints(inputPdf, appearance.PageNumber);
+            bottom = pageHeight - bottom - height;
+        }
+
+        return new PdfRectangle(left, bottom, left + width, bottom + height);
+    }
+
+    private static double GetPageHeightInPoints(Stream inputPdf, int pageNumber)
+    {
+        if (pageNumber <= 0)
+            throw new BadRequestException("Signature page number must be greater than zero.");
+
+        var previousPosition = inputPdf.CanSeek ? inputPdf.Position : 0;
+
+        try
+        {
+            if (inputPdf.CanSeek)
+                inputPdf.Position = 0;
+
+            using var processor = new PdfDocumentProcessor();
+            processor.LoadDocument(inputPdf);
+
+            var pageCount = processor.Document.Pages.Count;
+            if (pageNumber > pageCount)
+                throw new BadRequestException($"Signature page number {pageNumber} is out of range. Document has {pageCount} page(s).");
+
+            return processor.Document.Pages[pageNumber - 1].CropBox.Height;
+        }
+        finally
+        {
+            if (inputPdf.CanSeek)
+                inputPdf.Position = previousPosition;
+        }
+    }
+
     //TODO: verify and optimize (remove memory stream etc.) the check algortihm
     public async Task<PdfSignatureCheckResultDto> CheckPdfSignatureAsync(Stream inputPdf, CancellationToken cancellationToken = default)
     {