PHP 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. Chilkat2 PHP

<?php

use Chilkat2\JsonObject;
use Chilkat2\Pdf;

// 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 Pdf();
try {
    $pdf->LoadFile('qa_data/pdf/invoice_signed.pdf');
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

echo 'Signatures: ', $pdf->NumSignatures, "\n";

$json = new JsonObject();
$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 JsonObject();
try {
    $pdf->TextReplace('check', $json, $jsonOut);
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

echo 'check: ok = ', ($jsonOut->BoolOf('ok') ? 'true' : 'false'), "\n";

// "apply" is refused while PreserveSignatures is true (the default).
try {
    $pdf->TextReplace('apply', $json, $jsonOut);
} catch (\Chilkat2\Exception $e) {
    echo 'apply refused: ', $e->getMessage(), "\n";
}

// Allowing the signature to be broken:
$pdf->PreserveSignatures = false;
try {
    $pdf->TextReplace('apply', $json, $jsonOut);
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

echo 'applied: ', ($jsonOut->BoolOf('applied') ? 'true' : 'false'), "\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.
try {
    $pdf->WriteFile('qa_output/invoice_reissued_broken_signature.pdf');
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

echo 'Signatures after writing: ', $pdf->NumSignatures, "\n";
$sigInfo = new JsonObject();
try {
    $pdf->VerifySignature(0, $sigInfo);
    $validated = true;
} catch (\Chilkat2\Exception $e) {
    $validated = false;
}
echo 'Signature 0 verifies: ', ($validated ? 'true' : 'false'), "\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