Dart

PDF Signature Page Location

See more PDF Signatures Examples

This example demonstrates how to specify the location of a PDF signature on a page.

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);

  // When cryptographically signing a PDF, the signature's appearance can be placed on a specific
  // page in the PDF document, and at a specified location on the page.
  // The 1st page of the PDF document is page number 1 (we don't use 0-based numbering for PDF page numbers).
  // The PDF object has a NumPages property, so we can use it to sign on the last page of the PDF.
  json.updateInt('page', pdf.numPages);

  // appearance.y and appearance.x JSON properties control the x,y location of the signature.
  // The "appearance.y" can be "top" or "bottom".
  // The "appearance.x" can be "left", "middle", or "right".
  // It is also possible to specify exact PDF location in user space coordinates, which is discussed below.
  json.updateString('appearance.y', 'bottom');
  json.updateString('appearance.x', 'middle');

  // In this example, the fontScale (in combination with the number of appearance text lines and the length of the longest text line),
  // automatically determine the width/height of the signature text box. Any included graphic (JPG image or built-in SVG) is automatically
  // scaled to fit. It is alternatively possible to specify the desired width/height of the signature rectangle.  In that case
  // you would NOT specify a fontScale because Chilkat would automatically chose a font scale to fit the text to the desired rectangle.
  // This example demonstrates how to specify the exact width/height of the PDF signature text box.
  json.updateString('appearance.fontScale', '9.0');

  json.updateString('appearance.text[0]', 'Digitally signed by: cert_cn');
  json.updateString('appearance.text[1]', 'current_dt');
  json.updateString('appearance.image', 'document-accepted');
  json.updateString('appearance.imagePlacement', 'left');
  json.updateString('appearance.imageOpacity', '100');

  // Load the signing certificate. (Use your own certificate.)
  final cert = CkCert();
  try {
    cert.loadPfxFile('qa_data/pfx/myPdfSigningCert.pfx', 'pfx_password');
  } 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 here:

  // ----------------------------------------------------------------------------------------------------
  // *** Scroll down for information about specifying the PDF signature x,y location in user space coordinates.
  // ----------------------------------------------------------------------------------------------------

  // (image:https://example-code.com/images/bottom_middle_signature.jpg/endImage)

  // The x,y coordinates of a PDF page are in "user space", called "points", and there are 72 pointes per inch.
  // A PDF page (8.5" x 11") is 612 points wide and 792 points high.
  // The bottom left is at 0,0.    The top right is at 612,792.
  // 
  // To specify the location of a signature rectangle, the "appearance.y" is the y coordinate of the top of the signature rectangle,
  // and the "appearance.x" is the x coordinate of the left of the signature rectangle.
  // Therefore, to position the signature rectangle at the exact top/left of the page, we do this:

  json.updateString('appearance.y', '792');
  json.updateString('appearance.x', '0');

  json.updateString('appearance.text[0]', 'Digitally signed again by: cert_cn');
  json.updateString('appearance.text[1]', 'current_dt');
  json.updateString('appearance.image', 'document-accepted');
  json.updateString('appearance.imagePlacement', 'right');

  final pdf2 = CkPdf();
  pdf2.loadFile('qa_output/hello_signed.pdf');
  pdf2.setSigningCert(cert);

  try {
    pdf2.signPdf(json, 'qa_output/hello_signed2.pdf');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

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

  // Here we have the PDF with the signature just added at the exact top/left.
  // (image:https://example-code.com/images/pdf_signature_top_left.jpg/endImage)
}