PHP Extension 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. PHP Extension

<?php

include("chilkat.php");

$success = false;

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

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

$json = new CkJsonObject();
$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 = new CkJsonObject();
$success = $pdf->TextReplace('check',$json,$jsonOut);
if ($success == false) {
    print $pdf->lastErrorText() . "\n";
    exit;
}

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

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

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

print 'applied: ' . $jsonOut->BoolOf('applied') . "\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 == false) {
    print $pdf->lastErrorText() . "\n";
    exit;
}

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

?>