I know that this is really a Microsoft Access forum, but I am a word
processor by birth (almost), so...
I'm in Windows XP, your setup might be slightly different. Open your
document (or start a new blank one); click on File; then scroll down and
click on Page Setup; you'll see three tabs, click on the second one labelled
Paper. On Paper Size, click on the down arrow, then scroll down to highlight
the word Custom, then click to display the word Custom in the box. You're
done. OK your way out of all the boxes/menus. Then go ahead and edit or
create your document.
Don't forget to save it again after you change the paper size!
HTH.
In Peace, Max