How do I have a form fill in my own PDF = or can i load a pdf in a form to be filled in ?

If the PDF is a fillable PDF, it might be possible to import it to create a JotForm form:

https://www.jotform.com/help/548-How-Can-I-Import-My-Own-PDF-to-JotForm

If it is not a fillable PDF, it would be possible to add a link to download your PDF or use a PDF embedder widget to allow user to view the PDF:

https://widgets.jotform.com/widget/pdf_embedder

But wouldn't be possible to have user fill out the PDF directly in the form or have the form fill out your PDF.