Objective-C 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. Objective-C

#import <CkoPdf.h>
#import <CkoJsonObject.h>

BOOL success = NO;

//  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

CkoPdf *pdf = [[CkoPdf alloc] init];
success = [pdf LoadFile: @"qa_data/pdf/invoice_signed.pdf"];
if (success == NO) {
    NSLog(@"%@",pdf.LastErrorText);
    return;
}

NSLog(@"%@%d",@"Signatures: ",[pdf.NumSignatures intValue]);

CkoJsonObject *json = [[CkoJsonObject alloc] init];
[json UpdateString: @"labels[0].label" value: @"Invoice Number:"];
[json UpdateString: @"labels[0].value" value: @"INV-2026-0500"];

//  "check" reads only, so it works on a signed PDF.
CkoJsonObject *jsonOut = [[CkoJsonObject alloc] init];
success = [pdf TextReplace: @"check" jsonIn: json jsonOut: jsonOut];
if (success == NO) {
    NSLog(@"%@",pdf.LastErrorText);
    return;
}

NSLog(@"%@%d",@"check: ok = ",[jsonOut BoolOf: @"ok"]);

//  "apply" is refused while PreserveSignatures is true (the default).
success = [pdf TextReplace: @"apply" jsonIn: json jsonOut: jsonOut];
if (success == NO) {
    NSLog(@"%@%@",@"apply refused: ",pdf.LastErrorText);
}

//  Allowing the signature to be broken:
pdf.PreserveSignatures = NO;
success = [pdf TextReplace: @"apply" jsonIn: json jsonOut: jsonOut];
if (success == NO) {
    NSLog(@"%@",pdf.LastErrorText);
    return;
}

NSLog(@"%@%d",@"applied: ",[jsonOut BoolOf: @"applied"]);

//  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 == NO) {
    NSLog(@"%@",pdf.LastErrorText);
    return;
}

NSLog(@"%@%d",@"Signatures after writing: ",[pdf.NumSignatures intValue]);
CkoJsonObject *sigInfo = [[CkoJsonObject alloc] init];
BOOL validated = [pdf VerifySignature: [NSNumber numberWithInt: 0] sigInfo: sigInfo];
NSLog(@"%@%d",@"Signature 0 verifies: ",validated);

//  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