Ai-chan uses WPS Office. It doesn't edit the pdf itself (unless it does, but Ai-chan hasn't found the feature yet), but instead has a built in system to convert it into docx and vice versa. It does have a daily limit on how many times you can convert pdf to docx though.
hmm... As a linux user, GIMP serves me well when I want to edit the content of the images, including in PDFs. What do you want to do exactly? Editing the texts?
Depending on what you want to edit, Libre Office and open pdfs and edit them. Though do note you might need to look up what font is used in the pdf and install said font.
Personally I use the freeware CutePDF - it lets you "print" pdf to your computer (save as files) and I use Foxit Reader for viewing/some editing of pdfs.