Dart

PDF Signature with Background Image (Seal/Stamp/etc.)

See more PDF Signatures Examples

Demonstrates how to sign a PDF with an appearance that includes a background image, such as a seal, stamp, etc.

Note: This example requires Chilkat v9.5.0.85 or greater.

Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example requires the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  final pdf = CkPdf();

  // Load a PDF to be signed.
  // The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
  try {
    pdf.loadFile('qa_data/pdf/hello.pdf');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Options for signing are specified in JSON.
  final json = CkJsonObject();

  // In most cases, the signingCertificateV2 and signingTime attributes are required.
  json.updateInt('signingCertificateV2', 1);
  json.updateInt('signingTime', 1);

  // Put the signature on page 1, top left
  json.updateInt('page', 1);
  json.updateString('appearance.y', 'top');
  json.updateString('appearance.x', 'left');

  // Use a font scale of 10.0
  json.updateString('appearance.fontScale', '10.0');

  // In this example, the appearance of the digital signature will contain three lines:
  // 1) The signing certificate's common name
  // 2) The current date/time
  // 3) Some arbitrary text.
  // The keyword "cert_cn" is replaced with the Certificate's Subject Common Name.
  // The keyword "current_dt" is replaced with the current date/time.
  // Any number of appearance text lines can be added.
  json.updateString('appearance.text[0]', 'Digitally signed by: cert_cn');
  json.updateString('appearance.text[1]', 'current_dt');
  json.updateString('appearance.text[2]', 'The crazy brown fox jumps over the lazy dog.');

  // Load a JPG image to be shown with 30% opacity in the background.
  // (the image must be in the JPG format)
  // The sample university.jpb is available at https://example-code.com/images/university.jpg

  final jpgData = CkBinData();
  try {
    jpgData.loadFile('qa_data/jpg/university.jpg');
  } on ChilkatException {
    print('Failed to load the JPG image.');
    return;
  }

  try {
    pdf.setSignatureJpeg(jpgData);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Specify that we want to display the JPG image in the center with 30% opacity.
  json.updateString('appearance.image', 'custom-jpg');
  json.updateString('appearance.imagePlacement', 'center');
  json.updateString('appearance.imageOpacity', '30');

  // Load the signing certificate. (Use your own certificate.)
  final cert = CkCert();
  try {
    cert.loadPfxFile('qa_data/pfx/myPdfSigningCert.pfx', 'secret');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Tell the pdf object to use the certificate for signing.
  try {
    pdf.setSigningCert(cert);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    pdf.signPdf(json, 'qa_output/hello_signed.pdf');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('The PDF has been successfully cryptographically signed.');

  // The appearance of the signature appears in Adobe Acrobat as shown below.
  // The JPG is automatically scaled to the size of the signature based on the signature's font scale
  // and number of text lines.
  // (image:https://example-code.com/images/signature2.jpg/endImage)
}