What is a PDF form?
Definition
A PDF form is a PDF document designed to collect information: names, dates, choices, signatures. It may carry interactive fields that capture the values as data, or it may be a static page meant to be printed and completed by hand.
Interactive vs. static
Some PDF forms have real input fields you can type into, so the answers are captured as structured data. Others are just a printed layout: the questions are there, but nothing records what you write. The same document can exist in both forms.
Why the difference matters
Only an interactive form yields data a program can read back. A static form has to be made fillable first, with its inputs detected and real fields placed, before software can capture or pre-fill the answers.