Building order for a PDF

I’m completely new to building an app and began working on my welcome page and “setup acct” for an app to create a PDF form that will be emailed from the app. My question is should I build my PDF form first for the app or vice versa or does it not really matter?

The form is “simple” where certain boxes are checked and info like ages of equipment, dates, client info, signatures and inserting pics then the form is emailed to client.

I appreciate your time.

I am not 100% clear on the flow here. Is a PDF form really necessary? The information you would get from a form could be obtained from an equivalent on-line form? If the PDF has varying content or format that would be a different matter

I’ll be gathering info on a home’s systems and inputting it to populate a form and add specific pics. Each home is going to be different and I want to be able to email the signed form when done.
The intent is to automate filling out the form, adding additional systems and emailing it.