PDF-Signer

Adds your signature on top of the pages of an existing PDF: drawn, typed, or a picture of it.

The signed copy is the original PDF with an incremental update appended. The original bytes are left exactly as they were, and the signatures are added after them. Forms, links, bookmarks and anything else the PDF held survive untouched, including an earlier digital signature, which stays valid for the revision it signed.

This places a visible signature. It is not a cryptographic digital signature.

It comes in two forms that produce the same file:

• In the browser, as a page published with GitHub Pages. The PDF is read and signed on your own computer and never uploaded.
• In PHP, as a command-line script and a library, with no Composer dependencies beyond PHP's gd and zlib extensions.

In the browser

1. Open the site, and choose or drop a PDF.
2. Make a signature. You can Draw it with a mouse, pen or finger, Type it in a handwriting font or plain text for dates and initials, or Upload a picture of it, with the white paper made transparent.
3. Choose the signature, then click where it goes on a page. Drag it to move it, drag its corner to resize it, and use × to remove it. With the keyboard, the arrow keys move it, + and - resize it, and Delete removes it.
4. Click Download signed PDF.

Signatures are kept in the page until it is closed. Tick Remember my signatures in this browser to keep them, stored in this browser only.

A PDF that is encrypted or password-protected is refused, since adding to it would damage it. For a PDF that is already digitally signed, you're told that viewers will report it changed after it was signed.

The page is plain HTML and JavaScript modules in web/, with no build step. Pages are displayed with pdf.js, loaded from cdnjs and checked against pinned SHA-384 hashes before it runs; the signing itself is this repository's own code.

The Publish site workflow publishes the site to the gh-pages branch whenever web/ or src/ changes on main, and on each release. The signer is the site's root page; the PHP class reference is under /reference/. To serve it, set Settings → Pages → Source to Deploy from a branch, with gh-pages and / (root).

To try it locally, serve the folder, since browsers only load modules over HTTP:

php -S 127.0.0.1:8080 -t web

PHP requirements

• PHP 8.1 or later.
• The gd and zlib extensions. On Windows, gd may need extension=gd enabled in php.ini; php -m lists what is loaded.

Command line

php bin/sign-pdf lease.pdf signature.png --at=3:72:640:160

This writes lease-signed.pdf beside the document and prints its path. Each --at=PAGE:X:Y:WIDTH places the signature once. X and Y are its top-left corner, in points from the top-left of the page as displayed, after any rotation or crop. WIDTH is its width in points; its height keeps the image's proportions. Repeat --at to sign several places.

• --remove-white makes a photographed signature's white paper transparent and trims it to the ink.
• --output=signed.pdf chooses where the copy goes.

The script exits with 1 and a message on standard error when something goes wrong, such as a missing page or an encrypted PDF.

Library

use PdfSigner\SignatureImage;
use PdfSigner\Signer;

$signature = SignatureImage::fromFile('signature.jpg')->withoutWhiteBackground()->trimmed();

Signer::open('lease.pdf')
    ->stamp($signature, page: 3, x: 72, y: 640, width: 160)
    ->stamp($signature, page: 5, x: 72, y: 700, width: 160)
    ->save('lease-signed.pdf');

• Signer::pageCount() and pageSize($page) give each page's displayed size in points.
• hasDigitalSignatures() says whether the PDF was already digitally signed.
• stampWithMatrix() takes a transformation matrix in the page's own coordinates, for callers that work those out themselves.
• open() and fromString() throw a PdfSigner\Pdf\EncryptedPdfException for an encrypted PDF, and a PdfException for one that can't be read.

How it works

• PdfSigner\Pdf\Document reads just enough of a PDF to revise it. It follows the chain of cross-reference sections, both classic tables and the compressed streams modern writers use, and reads objects packed into object streams. It walks the page tree with the attributes pages inherit. Where an offset is wrong, it finds objects by scanning the file, as PDF viewers do.
• Each signed page gets a new revision. Its own content is wrapped in q … Q, so a transformation it leaves behind can't move the signature. The signature is drawn after it, and the page's resources name the signature image.
• PdfSigner\Pdf\IncrementalUpdate appends the new objects with a cross-reference section of the same kind the file already uses, whose /Prev points back to the previous one.
• web/ holds the same code in JavaScript, and the two produce the same PDF, object for object. Only the compressed image bytes can differ, since browsers and PHP ship different builds of zlib.

Tests

composer install
composer test

The browser version's tests use Node's built-in test runner and need Node 22 or later:

composer test-web

Coding standards and documentation

The PHP code is formatted with php-cs-fixer, using .php-cs-fixer.dist.php; the Coding Standards workflow fails a push that isn't formatted.

composer cs

The class reference is built with phpDocumentor from phpdoc.dist.xml into build/reference/. To build it locally, install phpDocumentor (for example with phive install phpDocumentor) and run it from the repository root:

tools/phpDocumentor --config phpdoc.dist.xml