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VB.NET

PDF Sign Under Existing Signature

See more PDF Signatures Examples

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.

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VB.NET 
Dim success As Boolean = False

'  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.
success = 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.)

'  image

'  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:

'  image