Unfortunately, PDF format was not made for editing. Comparing to RTF, Doc/Docx and .text it was created initially for publishing and printing. So, editing of existing PDF documents is a tricky task and more like adding something or removing something ! Obviously, there are apps today allowing you to do some editing, here are some of them. Online Pdf Editing (paid) - this paid downloadable app was made by Online Pdf Editing company, that invented PDF in a first place. Foxit Editor (paid) - this paid downloadable app was made by Foxit that also made free pdf viewer alternative to Online Pdf Editing . PDFLite.co (free version) - this online app with pdf editor, pdf protection, pdf merging and splitting requires no downloads and works completely in your browser providing the same 100% privacy for data as offline downloadable apps.
Now this is really useful. You can also use this PDF editor for writing your own PDF files. So, we see how popular PDF is. And the popularity of PDF documents is rising day by day.