I usually get something like this from professors, "Please put your topic suggestions into a Micsosoft Word (or Word-comatible) document, and send the document to me as an email attachment." For this particular assignment it was just a few research topics we might like to do our final paper on, and I did write that out in Pages. I then copy/pasted into Word, and the formatting was messed up. So when professors prefer Word I just tend to write the assignment in Word to avoid any issues.
A PDF would probably be ok for some but I am used to defaulting to Word at this point, and don't want to take chances.
Why would you do this? Why not go to File > Export in Pages and export the doc to a Word file?