PDF digital signature validation in C# and VB.NET
PDF digital signature validation primarily checks that:
- The document has not been modified since the signature was applied.
- The signer's identity is valid.
With GemBox.Pdf, you can validate that the PDF document has not been modified since the signature was applied in your C# or VB.NET application.
The following example shows how to validate all signatures in the PDF document.
using System;
using GemBox.Pdf;
using GemBox.Pdf.Forms;
class Program
{
static void Main()
{
// If using the Professional version, put your serial key below.
ComponentInfo.SetLicense("FREE-LIMITED-KEY");
using (var document = PdfDocument.Load("%InputFileName%"))
{
foreach (var field in document.Form.Fields)
if (field.FieldType == PdfFieldType.Signature)
{
var signatureField = (PdfSignatureField)field;
var signature = signatureField.Value;
if (signature != null)
{
var signatureValidationResult = signature.Validate();
if (signatureValidationResult.IsValid)
{
Console.Write("Signature '{0}' is VALID, signed by '{1}'. ", signatureField.Name, signature.Content.SignerCertificate.SubjectCommonName);
Console.WriteLine("The document has not been modified since this signature was applied.");
}
else
{
Console.Write("Signature '{0}' is INVALID. ", signatureField.Name);
Console.WriteLine("The document has been altered or corrupted since the signature was applied.");
}
}
}
}
}
}
Imports System
Imports GemBox.Pdf
Imports GemBox.Pdf.Forms
Module Program
Sub Main()
' If using the Professional version, put your serial key below.
ComponentInfo.SetLicense("FREE-LIMITED-KEY")
Using document = PdfDocument.Load("%InputFileName%")
For Each field In document.Form.Fields
If field.FieldType = PdfFieldType.Signature Then
Dim signatureField = CType(field, PdfSignatureField)
Dim signature = signatureField.Value
If signature IsNot Nothing Then
Dim signatureValidationResult = signature.Validate()
If signatureValidationResult.IsValid Then
Console.Write("Signature '{0}' is VALID, signed by '{1}'. ", signatureField.Name, signature.Content.SignerCertificate.SubjectCommonName)
Console.WriteLine("The document has not been modified since this signature was applied.")
Else
Console.Write("Signature '{0}' is INVALID. ", signatureField.Name)
Console.WriteLine("The document has been altered or corrupted since the signature was applied.")
End If
End If
End If
Next
End Using
End Sub
End Module
Note that the validity of the signer's identity is currently not checked. This feature will be implemented in future versions of GemBox.Pdf, based on user feedback.
