PureBasic Requires Chilkat v11.7.0+

Optimizing a Signed PDF (PreserveSignatures)

See more PDF Optimization Examples

Demonstrates what happens when a signed PDF is optimized. Optimizing rewrites the document, and a rewrite breaks every existing digital signature, so with PreserveSignatures true (the default) Optimize refuses and LastErrorText says why. Setting PreserveSignatures to false allows it, and the signature that was in the file no longer verifies afterwards. "audit" is always allowed, because it changes nothing. PureBasic

IncludeFile "CkPdf.pb"
IncludeFile "CkJsonObject.pb"

Procedure ChilkatExample()

    success.i = 0

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

    ;  The PDF used in this example is available at invoice_signed.pdf

    pdf.i = CkPdf::ckCreate()
    If pdf.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPdf::ckLoadFile(pdf,"qa_data/pdf/invoice_signed.pdf")
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf)
        CkPdf::ckDispose(pdf)
        ProcedureReturn
    EndIf

    Debug "signatures: " + Str(CkPdf::ckNumSignatures(pdf))

    json.i = CkJsonObject::ckCreate()
    If json.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    jsonOut.i = CkJsonObject::ckCreate()
    If jsonOut.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ;  An audit changes nothing, so it is allowed on a signed PDF.
    success = CkPdf::ckOptimize(pdf,"audit",json,jsonOut)
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf)
        CkPdf::ckDispose(pdf)
        CkJsonObject::ckDispose(json)
        CkJsonObject::ckDispose(jsonOut)
        ProcedureReturn
    EndIf

    Debug "audit ok, estimated savings: " + Str(CkJsonObject::ckIntOf(jsonOut,"estimatedSavings.total"))

    ;  Optimizing is refused while PreserveSignatures is true.
    success = CkPdf::ckOptimize(pdf,"optimize",json,jsonOut)
    If success = 0
        Debug "Refused while PreserveSignatures is true."
    EndIf

    ;  Allow the rewrite.  Do this only when the signatures no longer matter -- an invoice being
    ;  archived, say, where the signed original is kept elsewhere.
    CkPdf::setCkPreserveSignatures(pdf, 0)
    success = CkPdf::ckOptimize(pdf,"optimize",json,jsonOut)
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf)
        CkPdf::ckDispose(pdf)
        CkJsonObject::ckDispose(json)
        CkJsonObject::ckDispose(jsonOut)
        ProcedureReturn
    EndIf

    success = CkPdf::ckWriteFile(pdf,"qa_output/invoice_optimized.pdf")
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf)
        CkPdf::ckDispose(pdf)
        CkJsonObject::ckDispose(json)
        CkJsonObject::ckDispose(jsonOut)
        ProcedureReturn
    EndIf

    Debug "optimized, bytesSaved: " + Str(CkJsonObject::ckIntOf(jsonOut,"bytesSaved"))

    ;  The signature is still in the file, but it no longer verifies: the bytes it covered have changed.
    pdf2.i = CkPdf::ckCreate()
    If pdf2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPdf::ckLoadFile(pdf2,"qa_output/invoice_optimized.pdf")
    If success = 0
        Debug CkPdf::ckLastErrorText(pdf2)
        CkPdf::ckDispose(pdf)
        CkJsonObject::ckDispose(json)
        CkJsonObject::ckDispose(jsonOut)
        CkPdf::ckDispose(pdf2)
        ProcedureReturn
    EndIf

    Debug "signatures after: " + Str(CkPdf::ckNumSignatures(pdf2))

    sigInfo.i = CkJsonObject::ckCreate()
    If sigInfo.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    verified.i = CkPdf::ckVerifySignature(pdf2,0,sigInfo)
    Debug "verifies after optimizing: " + Str(verified)


    CkPdf::ckDispose(pdf)
    CkJsonObject::ckDispose(json)
    CkJsonObject::ckDispose(jsonOut)
    CkPdf::ckDispose(pdf2)
    CkJsonObject::ckDispose(sigInfo)


    ProcedureReturn
EndProcedure