Can we link existing form with existing PDF?

If I have a form already created, and I want to have the answers fill a PDF that is also already created, can I link the two? Or do I have to build a new form from the PDF.

Unfortunately, this is not currently possible to link an existing form to an existing PDF. You will need to import a PDF to get a new connected form.

Although, you can create JotForm PDF Documents for your existing forms:

Introducing JotForm PDF Editor - Turn form responses into designed PDFs