Signing a document with a digital signature

Product Version Product Author
2020.1.310 RadPdfProcessing Martin Velikov

Description

How to sign a document with a digital signature using FixedContentEditor.

Solution

In order to sign a PDF file with the PdfProcessing library, you need an instance of the System.Security.Cryptography.X509Certificates.X509Certificate2 class. One way to create such an instance is to provide the path to a PFX file and the password in an X509Certificate2 constructor, as in the provided example.

PdfFormatProvider provider = new PdfFormatProvider(); 
RadFixedDocument document = ImportDocument(); 
string certificateFilePath = "Resources/JohnDoe.pfx"; 
string certificateFilePassword = "johndoe"; 
 
// Define the certificate which will be used for the signing.  
X509Certificate2 certificate = 
    new X509Certificate2(certificateFilePath, certificateFilePassword); 
 
// The name of the signature must be unique.  
string signatureName = "SampleSignature"; 
 
// This is the Form XObject element that represents the contents of the signature field.  
Form form = new Form(); 
form.FormSource = new FormSource(); 
form.FormSource.Size = new Size(120, 120); 
 
// We will use the editor to fill the Form XObject.  
FixedContentEditor formEditor = new FixedContentEditor(form.FormSource); 
formEditor.DrawCircle(new Point(50, 50), 20); 
formEditor.DrawText(signatureName); 
 
// The Signature object is added to a signature field, so we can add a visualization to it.  
SignatureField signatureField = new SignatureField(signatureName); 
signatureField.Signature = new Signature(certificate); 
 
// The widget contains the Form XObject and defines the appearance of the signature field.  
SignatureWidget widget = signatureField.Widgets.AddWidget(); 
widget.Rect = new Rect(new Point(200, 600), new Size(100, 100)); 
widget.Border = new AnnotationBorder(100, AnnotationBorderStyle.Solid, null); 
widget.Content.NormalContentSource = form.FormSource; 
 
// The Widget class inherits from Annotation. And, as any other annotation, must be added to the respective collection of the page.  
RadFixedPage page = document.Pages.AddPage(); 
page.Annotations.Add(widget); 
document.AcroForm.FormFields.Add(signatureField); 
However, there are other approaches provided by the .Net Framework API that allow you to get an X509Certificate2 class instance. The following code snippet demonstrates a possible approach for getting an X509Certificate2 class instance from a external devise (e.g. USB token or hardware security module (HSM)) using .Net Framework API:

X509Store store = new X509Store(StoreLocation.CurrentUser); 
store.Open(OpenFlags.ReadOnly); 
X509Certificate2Collection sel = X509Certificate2UI.SelectFromCollection(store.Certificates, null, null, X509SelectionFlag.SingleSelection); 
 
X509Certificate2 cert = sel[0]; 
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