If I understand you correctly, you propose to import PowerPoint files and PDFs and other static material into FCP and make a video from that. I assume a computer will drive the projector, and that you have no sound.
The way I would do it is to use Keynote – not FCP. Keynote looks a lot better than PowerPoint; you can place and resize graphics easily; and you can then export the presentation as a self-contained Quicktime 640×480 movie. Keynote can include a sprite track in the .mov file, if you wish, which will allow the presenter to change the slides within the file at the click of a mouse. If the computer driving the projector is a PC, it will work perfectly well using Quicktime for Windows.
I have done this successfully using a 50 ft screen, with a projector driven by a Dell. The only trick is to experiment with the compression settings to bring up the sharpness a bit.