I admit: I love to write technical documentations. It's an unusual habit of a developer to do so, but somehow I adore having something to look at after a while and still be able to understand what's going on. In the past I used several tools for that. What I can say is that word processors like MS Word are NOT suitable to write a decent documentation for software. Just do not use them. I recently discovered MkDocs as the tool of my choice. This allows you to create neat online documentation as well as printable PDFs using the right plugins.