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(VB.NET) PDF Sign Under Existing Signature
This example explains how sign a previously-signed PDF and place the signature appearance below the existing signature.
Note: This example requires Chilkat v9.5.0.85 or greater.
' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.
Dim pdf As New Chilkat.Pdf
' Load a PDF to be signed.
Dim success As Boolean = pdf.LoadFile("qa_data/pdf/sign_testing_4/hello_signed.pdf")
If (success = False) Then
Debug.WriteLine(pdf.LastErrorText)
Exit Sub
End If
' The PDF we'll be signing already has a signature added in Adobe Acrobat DC.
' It looks like this:
' (Notice the Adobe background logo, which is commonly what you'll see when a signature
' is created by Adobe Acrobat. Chilkat (obviously) does not create signatures using the Adobe
' logo because it would be a copyright violation.)
' Options for signing are specified in JSON.
Dim json As New Chilkat.JsonObject
' In most cases, the signingCertificateV2 and signingTime attributes are required.
json.UpdateInt("signingCertificateV2",1)
json.UpdateInt("signingTime",1)
' To put our new signature underneath the existing signature, we have to specify the page
' where the existing signature is found, and then we can specify "under" for the "appearance.y"
json.UpdateInt("page",1)
json.UpdateString("appearance.y","under")
json.UpdateString("appearance.fontScale","10.0")
json.UpdateString("appearance.text[0]","Reason: Agreement Accepted by John")
json.UpdateString("appearance.text[1]","Date: current_dt")
' Load the signing certificate. (Use your own certificate.)
Dim cert As New Chilkat.Cert
success = cert.LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx","secret")
If (success = False) Then
Debug.WriteLine(cert.LastErrorText)
Exit Sub
End If
' Tell the pdf object to use the certificate for signing.
success = pdf.SetSigningCert(cert)
If (success = False) Then
Debug.WriteLine(pdf.LastErrorText)
Exit Sub
End If
' Note: When adding an additional signature to a PDF, the existing signatures
' are validated, and this includes validating the certificates previously used to
' create the existing signatures. (A signature typically embeds the signing certs.)
' In some cases, the certificates and/or certs in the chain of authentication for
' existing signatures are not present, and are not available on the current system.
' In this case, you can skip the validation by setting this keyword in UncommonOptions:
pdf.UncommonOptions = "NO_VERIFY_CERT_SIGNATURES"
success = pdf.SignPdf(json,"qa_output/hello_signed.pdf")
If (success = False) Then
Debug.WriteLine(pdf.LastErrorText)
Exit Sub
End If
Debug.WriteLine("The PDF has been successfully cryptographically signed.")
' Here's a screenshot of the 2nd signature positioned under the 1st in Adobe Acrobat:
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