Wordpress - Custom with no plugins - Signature integration

WHAT WE HAVE NOW We have a Wordpress website with a subscription form This is not handled by any plugin, it’s pure custom HTML + PHP + JS code in the page template itself. It lets you subscribe and the form gets posted the script (in the Wordpress page template) writes some data in the db (in a custom table), and it redirects you to Paypal and when you get back from Paypal it lands on another Wordpress page with another custom template with pure PHP code in it. This paypal landing page template will create a pdf with all the data from the form filled in. WHAT WE NEED We want to integrate in the initial form something like this [login to view URL] (you may have better ideas, we need this to work on every device, also mobile with touch) The signature must be at the end of the form and must be completed before going to the payment step The signature must be saved to an image on the server and the path to it must be saved in the database, using a new field in the table we already have. After the payment, when we generate the pdf (we already do that as said above) with the customer data, the signature should be applied on the document as well (there is a blank spot with a line, the signature should go there). Please note that we have two different possible PDFs, one page per each - nothing fancy, with a slightly different position for the signature.