Prepopulate Fillable/Signable PDF from normal form

Frustrating as all else. I need a form that's submitted to create a e-signable pdf. Seems simple, but it seems developers I hire say they can do it, but simply cannot.

I'm confident I'm close; I'd rather not have to go to yet another monthly software to simply have a form populate a PDF, ready for signing.. upon signing, I need that to be another 'form submission', so I can tag them appropriately through zapier.

If I understood correctly you want to pass the data from the submitted online form to a Fillable PDF Form. That is not possible. 

You can only pass the data from an online form to another online form. 

How to Automatically Pass Form Data to Another Form

If you want to allow your users to sign your form, you can add an E-Signature field to your form and then create a PDF report using our PDF Editor. 

How to Add an E-Signature to Your Form