To determine if a PDF file is meant to be an interactive form, examine the file for the presence of form fields, or areas in the document that ask for information such as name, address, preference, etc. Boxes or fields drawn on the page can also indicate that the document is meant to function as a form. If the form is to be completed online, rather than on paper, then the form is meant to be an interactive form, and the form elements must be made accessible. Even when a form is meant to be filled out on paper, it can be very beneficial to users with disabilities to provide the form in electronic format with accessible forms. For example, this will allow users who are blind or visually impaired to fill out the form electronic privately, even if it is not submitted electronically.
The Make Accessible Wizard contains a command to Detect Form Fields and Set Tab Order to follow the document structure. The wizard will ask if the document is meant to be a fillable form, and then it will automatically detect form fields.
Please refer to the document Acrobat DC Accessible Forms for instructions on how to make electronic forms accessible to people with disabilities. This document provides instructions for creating form fields manually or making form fields accessible after automatic detection.