Ok. The PDF file format itself is not very good to open the file for editing. A PDF file is really good for viewing, a exchange format which can be opened everywhere and which looks similar on each PC, but the information inside a PDF file is not really good for an editor. Opening a PDF file in an editor would often be very inaccurate. Word and other text applications do a much better job here.
It's always a good choice to have an application for editing. Always export a PDF file if you want to share your file.