OPEN RECENT FILES
Fortunately, you don’t have to live with just four recently used files. You can choose any number up to nine. Here’s how: Choose Tools, Options, and click the General tab. (In Office 11, it is Word, Preferences and General)
In the box to the right of ‘Recently used files list,’ (or 'Track Recently Opened Documents' in Office 11) type the number of files you’d like your File menu to display (or use the little arrows to increase or decrease the number). Click OK to lock in your choice. If you’ve increased the number, you’ll need to open more than four files to notice the change.