(Tcl) 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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load ./chilkat.dll

# This example requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

set pdf [new_CkPdf]

# Load a PDF to be signed.
set success [CkPdf_LoadFile $pdf "qa_data/pdf/sign_testing_4/hello_signed.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    exit
}

# 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.
set json [new_CkJsonObject]

# In most cases, the signingCertificateV2 and signingTime attributes are required.
CkJsonObject_UpdateInt $json "signingCertificateV2" 1
CkJsonObject_UpdateInt $json "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"
CkJsonObject_UpdateInt $json "page" 1
CkJsonObject_UpdateString $json "appearance.y" "under"

CkJsonObject_UpdateString $json "appearance.fontScale" "10.0"

CkJsonObject_UpdateString $json "appearance.text[0]" "Reason: Agreement Accepted by John"
CkJsonObject_UpdateString $json "appearance.text[1]" "Date: current_dt"

# Load the signing certificate. (Use your own certificate.)
set cert [new_CkCert]

set success [CkCert_LoadPfxFile $cert "qa_data/pfx/myPdfSigningCert.pfx" "secret"]
if {$success == 0} then {
    puts [CkCert_lastErrorText $cert]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkCert $cert
    exit
}

# Tell the pdf object to use the certificate for signing.
set success [CkPdf_SetSigningCert $pdf $cert]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkCert $cert
    exit
}

# 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:
CkPdf_put_UncommonOptions $pdf "NO_VERIFY_CERT_SIGNATURES"

set success [CkPdf_SignPdf $pdf $json "qa_output/hello_signed.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkCert $cert
    exit
}

puts "The PDF has been successfully cryptographically signed."

# Here's a screenshot of the 2nd signature positioned under the 1st in Adobe Acrobat:



delete_CkPdf $pdf
delete_CkJsonObject $json
delete_CkCert $cert