Add Digital Signatures on an existing page | Telerik Document Processing

Product Version	Product	Author
2021.1.118	RadPdfProcessing	Georgi Georgiev

Description

A common scenario is to replace a temporary page content (a templated text) with a Digital Signature widget. This allows already created PDF documents, e.g. using the Telerik Report Designer, to be modified by adding a Digital Signature on a position defined by the existing content of the document.

Solution

The following example demonstrates the approach of iterating the page content and finding TextFragment elements matching the $CollectSignature text. For each found match, a Signature Field is created and the TextFragment is replaced with a Signature widget. The Rect property is used to position and outline the Signature widget on the page.

foreach (RadFixedPage page in document.Pages) 
{ 
    List<TextFragment> contentToRemove = new List<TextFragment>(); 
 
    foreach (ContentElementBase contentElement in page.Content) 
    { 
        // Find a TextFragment excactly mathcing the $CollectSignature text 
        if (contentElement is TextFragment textFragment && textFragment.Text == "$CollectSignature") 
        { 
            // Create and add Signature Field and Signature Widget 
            SignatureField signatureField = document.AcroForm.FormFields.AddSignature("SignatureFieldUniqueName"); 
            SignatureWidget widget = signatureField.Widgets.AddWidget(); 
 
            Point location = new Point(textFragment.Position.Matrix.OffsetX, textFragment.Position.Matrix.OffsetY - textFragment.FontSize); 
            widget.Rect = new Rect(location, new Size(DesiredWidth, DesiredHeight)); 
 
            page.Annotations.Add(widget); 
 
            // Indicate the TextFragment to be removed 
            contentToRemove.Add(textFragment); 
        } 
    } 
 
    foreach (TextFragment contentElement in contentToRemove) 
    { 
        page.Content.Remove(contentElement); 
    } 
}