I created a couple of PDF files that you can use for testing. TripInfo.pdf is a regular PDF without any form field. TripInfo (Form).pdf has a few Text Fields and a couple of Check Box. You can see the form field names in the screenshot TripInfo.png.

RayHopefield wrote:

Can we assume that the pdf that will be used with software have form fields already?

Yes, if you have to, though I don't think it's necessary because your code will process the PDF file and return, presumably, a list of form fields. If there's no form field in the PDF, it simply returns an empty list.