Normally documents are shared across the web in pdf format. This is because if a document is shared in any other format, there are chances that it will be modified in the way by someone or it will be displayed differently in different readers on different operating systems.
But with pdf, it will remain same no matter what software you use to open it, or if you are on Linux, Mac OS or Windows. Its also relatively difficult to modify a pdf document in transit as one may have to first remove password from pdf document to edit it.
So you will probably get most of your documents in pdf format. But once you get it, you may want to convert pdf to Word format or plain text format to edit it as needed.
You can use First PDF to convert a pdf to Word document or a text document easily. Just open a pdf file in First PDF, select the output format, see the output preview and convert. You can also convert pdf to image using this software.
You can batch convert multiple pdf files using this software. And the best thing about it is that its free. Download First PDF from this link.