I am doing my documentation project and I want to know if I can fill my documentation with dummy text.
Sure. I’ve seen lots of projects, including some very polished pages, use placeholder text and images.
Sure, you can do that, but (gonna go ahead and shamelessly quote myself here)…
You could always write a documentation page about the history and uses of Lorem Ipsum text. 
FYI, Lorem Ipsum isn’t nonsense, it’s part of a speech by Cicero.