Dart

PDF Sign Unsigned Signature Field

See more PDF Signatures Examples

Demonstrates how to sign a PDF's unsigned signature field.

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 containing an unsigned signature field.
  try {
    pdf.loadFile('qa_data/pdf/unsigned_sig_field/due_diligence.pdf');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // A PDF with an unsigned signature field appears in Adobe Acrobat as shown below.
  // (When the mouse pointer is hovered over the field, a tooltip will likely show a message
  // such as "Unsigned signature field (Click to sign)".  
  // This example code will automatically find the unsigned signature field,
  // and signs using your certificate.  It automatically sizes the text to the space alotted
  // for the signature.
  // (image:https://example-code.com/images/unsignedSigField.jpg/endImage)

  // 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);

  // We don't specify the page or a specific location because Chilkat will automatically
  // find the unsigned signature field and use its location and size and will scale the
  // signatures visual appearance (text + graphics) to the correct size required to fit.
  // We only need to indicate the desire to fill the unsigned signature field.
  json.updateBool('appearance.fillUnsignedSignatureField', true);

  // Starting in Chilkat v9.5.0.90, if a PDF contains multiple unsigned signature fields,
  // the field to be signed can be chosen by name:
  // To list unsigned signature fields, see this example: List PDF Unsigned Signature Fields
  json.updateString('unsignedSignatureField', 'doctor_signature');

  // Note: If the PDF document contains multiple unsigned signature fields, Chilkat will 
  // sign the 1st one found. 

  // 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.');

  // This signature will include one of the built-in SVG graphics (green-check-grey-circle).
  json.updateString('appearance.image', 'green-check-grey-circle');
  json.updateString('appearance.imagePlacement', 'left');

  // 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/due_diligence_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.
  // (image:https://example-code.com/images/signature3.jpg/endImage)
}