How to use CTRL+F to find words in full-screen mode?

I love writing in full-screen mode when I need to focus on just the manuscript, but I can’t use CTRL+F to find words while in full-screen mode, and must return to normal mode to use that feature. Why is that? How can I search for words within the document I’m working on while in full-screen mode? (I’m not talking about keyword search. I’m talking about the basic find/replace feature that all word-processor’s have.)