Perl Requires Chilkat v11.7.0+

Replace Text in a Signed PDF (PreserveSignatures)

See more PDF Text Replacement Examples

Applying a text replacement rewrites the page content, which invalidates any digital signature on the PDF. While the PreserveSignatures property is true (the default), "apply" is refused on a signed PDF; "check" only reads and is always allowed. Setting PreserveSignatures to false allows the replacement; the signature field stays in the written PDF but no longer verifies, so the document should be signed again afterwards if a signature is wanted. Perl

use chilkat();

$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

$pdf = chilkat::CkPdf->new();
$success = $pdf->LoadFile("qa_data/pdf/invoice_signed.pdf");
if ($success == 0) {
    print $pdf->lastErrorText() . "\r\n";
    exit;
}

print "Signatures: " . $pdf->get_NumSignatures() . "\r\n";

$json = chilkat::CkJsonObject->new();
$json->UpdateString("labels[0].label","Invoice Number:");
$json->UpdateString("labels[0].value","INV-2026-0500");

#  "check" reads only, so it works on a signed PDF.
$jsonOut = chilkat::CkJsonObject->new();
$success = $pdf->TextReplace("check",$json,$jsonOut);
if ($success == 0) {
    print $pdf->lastErrorText() . "\r\n";
    exit;
}

print "check: ok = " . $jsonOut->BoolOf("ok") . "\r\n";

#  "apply" is refused while PreserveSignatures is true (the default).
$success = $pdf->TextReplace("apply",$json,$jsonOut);
if ($success == 0) {
    print "apply refused: " . $pdf->lastErrorText() . "\r\n";
}

#  Allowing the signature to be broken:
$pdf->put_PreserveSignatures(0);
$success = $pdf->TextReplace("apply",$json,$jsonOut);
if ($success == 0) {
    print $pdf->lastErrorText() . "\r\n";
    exit;
}

print "applied: " . $jsonOut->BoolOf("applied") . "\r\n";

#  The written PDF is a full rewrite with the replacement.  The signature field is still in the document,
#  but the bytes it signed are gone, so it no longer verifies.
$success = $pdf->WriteFile("qa_output/invoice_reissued_broken_signature.pdf");
if ($success == 0) {
    print $pdf->lastErrorText() . "\r\n";
    exit;
}

print "Signatures after writing: " . $pdf->get_NumSignatures() . "\r\n";
$sigInfo = chilkat::CkJsonObject->new();
$validated = $pdf->VerifySignature(0,$sigInfo);
print "Signature 0 verifies: " . $validated . "\r\n";

#  Sample output:

#  Signatures: 1
#  check: ok = true
#  apply refused: ChilkatLog:
#    TextReplace:
#      DllDate: Nov  7 2026
#      ChilkatVersion: 11.7.0
#      UnlockPrefix: CHLKAT
#      UnlockStatus: 2
#      Architecture: Little Endian; 64-bit
#      Language: Visual C++ 11.0 / x64
#      VerboseLogging: 0
#      replaceTextOp:
#        op: apply
#        The PDF is signed: replacing text rewrites the content and invalidates the signatures (set PreserveSignatures = false to allow it).
#      --replaceTextOp
#      Failed.
#    --TextReplace
#  --ChilkatLog
#  
#  applied: true
#  Signatures after writing: 1
#  Signature 0 verifies: false