Can you give me a little more detail of what you are trying to accomplish? What is the PDF, is it a form? Is the form not "fillable", when you open the form in Adobe Reader does it show what looks like form fields but you can't click into them? Is the PDF secured so you cannot edit it?
Are you hoping to create an "online form" from the PDF, or use the "Import a PDF" feature in FormsCentral? Do you just want to take a PDF that has form fields but is not fillable and add the form fields to the PDF?
The more information you can give about your workflow the better and you can send the PDF in question to me at firstname.lastname@example.org so I can give you more information.