How can I digitally sign PDFs created dynamically in PHP?

I need to take a PDF, add some dynamically generated license text to it, and digitally sign the document before emailing it to the intended recipient. What's the best way开发者_StackOverflow to do this in PHP?

My understanding of digital signage is that the content of the PDF is converted into a hash, and some property of the document is set to this value. If the content when converted to a hash doesn't match the hash in that property, the document has been altered. Is this correct? What is the certificates discussed on this and this page?

Am I right to think that it isn't possible to edit an existing PDF with TCPDF, only to create a new one? Is SetaPDF Stamper and SetaPDF Signer a valid and good option?

Many thanks

The commercial PDFlib product contains a feature called "PLOP DS" that allows you to perform digital signature operations from PHP, as well as selling an incredibly complete set of PDF operations in their other libraries. You can read more about the feature set here, or download an evaluation version from here.

I im facing the same project. My research have take me to this:

https://github.com/open-eid/browser-extensions2

There is a lot of information about the design and how to implement the solution. I'm starting to digest all this so as soon as I get more information I will update my answer. Hope this give you a starting point for finding your solution.

The SetaPDF Signer is the WebServer part of the equation. Check out this example:

https://www.setasign.com/products/setapdf-signer/demos/lacuna-web-pki/#p-529