ok let's unpack this.
PDF is built in to the OS. You need not purchase additional software. Scanning can be accomplished with the phone itself, it works great. Printing a Word doc to PDF is also built-in. Finally, converting from PDF to Word is usually a silly thing to do. However, you could copy the text and paste it into a new word file to accomplish it.
PDFs are printouts. You aren't really meant to edit them, you should edit them in the app from which you are printing them (this is a very common misconception). Make sense?