Add Digital Signatures to a WPF PDF Viewer with a Click-to-Place eSign Workflow

TL;DR: Learn to implement digital signatures inside the Syncfusion WPF PDF Viewer using programmatic techniques. It covers adding a custom eSign button, capturing click positions, generating a signature image, and applying a certificate-based signature. It enables a smooth, secure in-app signing experience even though the viewer does not support signature creation through its UI.

Add a digital signature using Syncfusion WPF PDF Viewer and .NET PDF Library

This digital signing workflow is built around the following  four key steps:

Step 1: Add an eSign button to the toolbar

When the WPF PDF Viewer loads, you can inject a custom eSign button into the existing toolbar.

To keep the UI consistent, we will reuse the style and icon of an existing toolbar item, as shown in the following code.

private void PDFViewer_Loaded(object sender, RoutedEventArgs e)
{
    var toolbar = PDFViewer.Template.FindName("PART_Toolbar", PDFViewer) as DocumentToolbar;
    var stackPanel = toolbar.Template.FindName("PART_ToolbarStack", toolbar) as StackPanel;
    var defaultButton = (Button)((StackPanel)stackPanel.Children[^1]).Children[0];
    var eSignButton = GetButton((Path)defaultButton.Content, defaultButton);
    stackPanel.Children.Add(eSignButton);
}

The GetButton method is responsible for:

• Creating the new button,
• Applying the existing style, and
• Attaching the click event that activates the signing mode.

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Step 2: Capture the exact spot where the user clicks

Once the eSign button is clicked, a flag is set to indicate that the next mouse click should trigger signature placement. This will convert the mouse-click coordinates to page-relative positions using the WPF PDF Viewer’s built-in method. So, the signature lands exactly where the user clicked.

This ensures:

• Pixel‑perfect placement.
• Support for multi‑page PDFs.
• A natural “click‑to‑sign” feel users already expect.

Refer to the following code example.

private void PDFViewer_PageClicked(object sender, PageClickedEventArgs args)
{
      if (addSignature)
      {
          var pageIndex = PDFViewer.CurrentPageIndex - 1;
          var pagePoint = PDFViewer.ConvertClientPointToPagePoint(args.Position, pageIndex + 1);
          ApplySignature(pageIndex, pagePoint);
          addSignature = false;
      }
}

Step 3: Dynamically generate a signature image

Instead of a generic stamp, this solution creates a meaningful visual signature. It:

• Generates a runtime image block containing:
  • Signer name.
  • Date and time.
• Combines it with a handwritten‑style name image.
• Produces a polished eSign graphic every time.

The visual result meets professional and regulatory requirements.

private void CreateCurrentDataImage()
{
     string text = $"Digitally signed by John\nDate: {DateTime.Now:yyyy.MM.dd\nHH:mm:ss zzz}";
     using var bitmap = new Bitmap(200, 100);
     using var graphics = Graphics.FromImage(bitmap);
     graphics.FillRectangle(Brushes.White, 0, 0, 200, 100);
     graphics.DrawString(text, new Font("Arial", 9), Brushes.Black, new RectangleF(10, 10, 180, 80));
     bitmap.Save(filePath + "DigitalSignatureBlock.png", ImageFormat.Png);
}

private void CombineSignatureAndDataImage()
{
      using var nameImage = Image.FromFile(filePath + "John.png");
      using var signImage = Image.FromFile(filePath + "DigitalSignatureBlock.png");
      using var combinedImage = new Bitmap(nameImage.Width + signImage.Width, Math.Max(nameImage.Height, signImage.Height));
      using var g = Graphics.FromImage(combinedImage);
      g.DrawImage(nameImage, 0, 0);
      g.DrawImage(signImage, nameImage.Width, 0);
      combinedImage.Save(filePath + "ESign.png", ImageFormat.Png);
}

Step 4: Apply a certificate‑based digital signature

Here’s where security comes in. Using the .pfx certificate:

• A cryptographic digital signature is applied.
• Metadata is embedded (reason, location, contact information).
• The signature is rendered visually at the chosen location.

Then, the PDF is saved and reloaded, now officially signed. All of this happens programmatically and securely.

private void ApplySignature(int pageIndex, Point pagePoint)
{
      var page = PDFViewer.LoadedDocument.Pages[pageIndex] as PdfLoadedPage;
      var cert = new PdfCertificate(filePath + "PDF.pfx", "password123");
      var signature = new PdfSignature(PDFViewer.LoadedDocument, page, cert, "Signature");
      var image = new PdfBitmap(filePath + "ESign.png");
      signature.Bounds = new RectangleF((float)pagePoint.X, (float)pagePoint.Y, image.PhysicalDimension.Width, image.PhysicalDimension.Height);
      signature.ContactInfo = "[email protected]";
      signature.LocationInfo = "Honolulu, Hawaii";
      signature.Reason = "I am the author of this document.";
      signature.Appearance.Normal.Graphics.DrawImage(image, 0, 0);
      using var stream = new MemoryStream();
      PDFViewer.LoadedDocument.Save(stream);
      stream.Position = 0;
      PDFViewer.Load(stream);
}

Refer to the following image for visual clarity.

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What the final result looks like

Users simply:

1. Click the eSign button.
2. Click where they want the signature.
3. Instantly see a signed, verified PDF.

No pop‑ups. No exports. No external apps.

GitHub reference

Also, refer to the example for adding a digital signature using Syncfusion WPF PDF Viewer and .NET PDF Library on GitHub.

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Start creating secure, in‑app WPF PDF signing experiences today

Thanks for reading! With this approach, you can enable smooth, certificate‑based PDF signing directly inside your WPF app, no external tools, no broken workflows. By extending Syncfusion WPF PDF Viewer with custom UI actions and the Syncfusion .NET PDF library, you gain full control over signature placement, appearance, and security.

Whether you’re building enterprise document workflows or everyday desktop utilities, this pattern makes in‑app PDF signing both practical and reliable.

If you’re already a Syncfusion customer, you can download the setup from your license and downloads page. New users can start with a free 30-day trial.

You can also contact us through our support forum, support portal, or feedback portal for queries. We are always happy to assist you!

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