Do you mean the number of "Recent Documents"?
Click the Office Button (Top/left of window). Click Word Options, click the
Advanced Button. Scroll down to the Display section. In the "Show this numbe
rof Recent Documents" option, set the number to 0 and click OK. This will
clear the list. You can go back and reset the option to whatever number you
wish.
You'll notice that there is a Pushpin Icon to the right of each recent
document. If you click this push pin, that document will be permanently
pinned to that menu until you click the pushpin again to release it.