How do I turn an existing PDF into a editable form?

[css_]

How do I turn an existing PDF into an editable form?

[anneb25000799]

My ability to select a pdf and convert it to a form just disappeared yesterday. I worked 2 days ago and now nothing! Tried scanning, changing existing pdfs etc. It just won't open the file to allow for a form conversion. I have been doing this for years and it is an important part of my work. HELP!!!!!!!!!!!