Xbase++

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.

Xbase++

LOCAL nSuccess
LOCAL oPdf
LOCAL oJson
LOCAL oCert

nSuccess := 0

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

oPdf := CreateObject("Chilkat.Pdf")

//  Load a PDF to be signed.
nSuccess := oPdf:LoadFile("qa_data/pdf/sign_testing_4/hello_signed.pdf")
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    RETURN
ENDIF

//  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.
oJson := CreateObject("Chilkat.JsonObject")

//  In most cases, the signingCertificateV2 and signingTime attributes are required.
oJson:UpdateInt("signingCertificateV2", 1)
oJson: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"
oJson:UpdateInt("page", 1)
oJson:UpdateString("appearance.y", "under")

oJson:UpdateString("appearance.fontScale", "10.0")

oJson:UpdateString("appearance.text[0]", "Reason: Agreement Accepted by John")
oJson:UpdateString("appearance.text[1]", "Date: current_dt")

//  Load the signing certificate. (Use your own certificate.)
oCert := CreateObject("Chilkat.Cert")
nSuccess := oCert:LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx", "secret")
IF (nSuccess == 0)
    ? oCert:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oCert:destroy()
    RETURN
ENDIF

//  Tell the pdf object to use the certificate for signing.
nSuccess := oPdf:SetSigningCert(oCert)
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oCert:destroy()
    RETURN
ENDIF

//  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:
oPdf:UncommonOptions := "NO_VERIFY_CERT_SIGNATURES"

nSuccess := oPdf:SignPdf(oJson, "qa_output/hello_signed.pdf")
IF (nSuccess == 0)
    ? oPdf:LastErrorText
    oPdf:destroy()
    oJson:destroy()
    oCert:destroy()
    RETURN
ENDIF

? "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)

oPdf:destroy()
oJson:destroy()
oCert:destroy()