This is indeed a challenge; there are no services that I’m aware of where you can submit a PDF and have it transformed into an e-signing-capable document. All of the e-signature services use a template approach that allows them to bind digital signatures to the resulting document. This is a key requirement because third parties cannot have the ability to substitute either a document with a signature or a signature with a document. Indeed, they must control the binding of data and digital signature fields into a unified binary that cannot be easily modified.
As such, you probably need a process like this, a solution architecture that has worked well for many Airtable clients. Note the only two blue lines represent the manual steps - all other steps in the process are automated.
