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.

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:https://example-code.com/images/signed_once_with_adobe_acrobat.jpg/endImage)

' 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:https://example-code.com/images/signed_under_existing_signature.jpg/endImage)