If you need to edit a pdf and don't have the original document you can try to open it using Word.  Word will do its best to convert it.  If the document has a lot of graphics and/or special formatting it might not convert well though.

Here is more information about how to open a pdf using Word:  https://support.office.com/en-us/article/edit-a-pdf-b2d1d729-6b79-499a-bcdb-233379c2f63a 

Note: The converted document might not have a perfect page-to-page correspondence with the original. For example, lines and pages may break at different locations.