I recently purchased a PDF program so that I could edit documents for fax and email as an easy way to deal with a document for neatness and accuracy.
Posting this question in a typography forum doesn't make much sense, but I'll nonetheless try to answer your question.
First of all, PDF is a final form document format. It isn't an editable document format such as a Microsoft Word document.
Programs that display and print PDF files often provide rudimentary capabilities of doing very simple “touch up” types of edits to existing PDF files. None allow editing such as you would do with a word processing program or a graphic arts layout program.
Since you didn't provide any information as to which “PDF program” you “purchased” (actually, you most likely purchased a license; very little software is actually sold), we can't tell you how this unknown software can be used to edit a PDF file if it can do any editing at all.