1. View | Header and Footer. This puts you in the header pane and displays
the Header and Footer toolbar. If you want the page number in the footer,
click on the Switch Between Header and Footer button on the toolbar.

2. If the page number will be the only text in the header/footer, press
Ctrl+E to center the paragraph. If other text is wanted, you can use the
built-in center tab stop (Tab once to get to it). If you have changed the
document margins, you'll probably need to relocate the tab stops.

3. Click on the Insert Page Number button. You should see the page number.
If you see { PAGE } instead, press Alt+F9 to toggle field code display.

For more on page numbering, see
http://www.mvps.org/word/FAQs/Numbering/PageNumbering.htm

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Suzanne S. Barnhill
Microsoft MVP (Word)