Tcl 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. Tcl

load ./chilkat.dll

set success 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

set pdf [new_CkPdf]

set success [CkPdf_LoadFile $pdf "qa_data/pdf/invoice_signed.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    exit
}

puts "signatures: [CkPdf_get_NumSignatures $pdf]"

set json [new_CkJsonObject]

set jsonOut [new_CkJsonObject]

#  An audit changes nothing, so it is allowed on a signed PDF.
set success [CkPdf_Optimize $pdf "audit" $json $jsonOut]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jsonOut
    exit
}

puts "audit ok, estimated savings: [CkJsonObject_IntOf $jsonOut estimatedSavings.total]"

#  Optimizing is refused while PreserveSignatures is true.
set success [CkPdf_Optimize $pdf "optimize" $json $jsonOut]
if {$success == 0} then {
    puts "Refused while PreserveSignatures is true."
}

#  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_put_PreserveSignatures $pdf 0
set success [CkPdf_Optimize $pdf "optimize" $json $jsonOut]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jsonOut
    exit
}

set success [CkPdf_WriteFile $pdf "qa_output/invoice_optimized.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jsonOut
    exit
}

puts "optimized, bytesSaved: [CkJsonObject_IntOf $jsonOut bytesSaved]"

#  The signature is still in the file, but it no longer verifies: the bytes it covered have changed.
set pdf2 [new_CkPdf]

set success [CkPdf_LoadFile $pdf2 "qa_output/invoice_optimized.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf2]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jsonOut
    delete_CkPdf $pdf2
    exit
}

puts "signatures after: [CkPdf_get_NumSignatures $pdf2]"

set sigInfo [new_CkJsonObject]

set verified [CkPdf_VerifySignature $pdf2 0 $sigInfo]
puts "verifies after optimizing: $verified"

delete_CkPdf $pdf
delete_CkJsonObject $json
delete_CkJsonObject $jsonOut
delete_CkPdf $pdf2
delete_CkJsonObject $sigInfo