Don't even try it, you'll break your balls getting it right.
What with securing the PDF's to the appropriate standards, signing on site or off site and the regulations involved, verifying customer identities and preventing fraud, it's too big a job for a handful of guys with no experience in this field to do it properly.
My advice: find a company that actually makes this component (and that has a good name in the industry and has major industry clients) and work with them.
Why do I say this? I've just watched a bunch of guys do the very same thing here. Their 30 day project is now 6 months in and it still has loads of bugs, performance issues and missing functionality (3rd party software does much more, meets all of the regulations and ultimately would have been cheaper)..
More information available here:
How Digital Signatures Work | DocuSign[
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