If you don't see page numbers on the screen or under File > Print Preview, go to Document > Header and Footer Options. Make sure the Show Header box is checked:
If you do see page numbers on screen but not under File > Print Preview, the page number may be outside the printable area of the page.
1. Go to Document > Header and Footer;
2. If the page number field at the upper right is anchored to a tab stop in the ruler bar, drag that tab stop to the left a couple of ticks
3. If there is no tab stop, place your cursor to the right of the page number field and period below the ruler. Hit the space bar a couple of times to move the page number field to the left a couple of ticks.