PDF files

You can not do this. When you export a pages file into a PDF it maintains the original that you could edit and create another PDF. But you cannot edit PDF's with Pages. Editors to do so, are available and most cost money. I haven't checked lately but you could look at LibreOffice (open source and free) and see if it can modify PDF's.

846-AK wrote:

How do you convert a PDF file back to an editable file in Pages?

As noted you need a PDF editor to change PDFs. If you create documents in Pages, I would recommend saving the original Pages file and export it as a PDF. That way you can go back and edit the original if needed.