A document’s margin is the space between the edge of the paper and where the text begins. Ideal margins depend on many factors, including the document type, the need to limit the number of pages (for example, if you’re paying by the page to fax or copy a document), and the audience’s needs. Adjusting the margins can also control the perception of your document, making it look like it is longer or shorter than it actually is. Many a student who has been assigned a “three-page paper” has tried to get away with writing less by using large margins! (Of course, that generally doesn’t work because teachers know that trick.)
Word offers several sets of standard margin settings. Choose Page Layout-->Margins and then choose from the list.
Each preset has a value assigned to the four page sides. Usually, a document uses the same margin setting for opposite sides (the same value for top and bottom, and the same value for left and right). This isn’t a hard-and-fast rule, though. You might, for example, want extra space at the top of a page when you’re printing on stationery with a name and address preprinted at the top. And, if you’re going to bind your pages or use a three-hole punch for pages presented in a binder, you might want a larger margin.
If none of the choices on the list match what you want, choose Custom Margins from the bottom of the Margins menu and enter precise values in the Page Setup dialog box that appears.