The page size is the size you'll get when you print. The display size on
screen is the page size scaled to your screen display. Changing the display
size has no effect on how much information you can fit on the page.
You can: the quick methods for getting more information onto the page --
Jezebel has dealt with one possibility of your question. Another possibility
is that you are looking at the horizontal and vertical rulers and seeing the
7x9 document body that would result from 1" top and bottom margins and 0.75"
left and right margins. In particular, you might not be seeing the top and
bottom margins at all if you have the "white space" hidden (see http://sbarnhill.mvps.org/WordFAQs/WhiteSpace.htm).