Hi jc,
I don't think "Background" is a useful choice here. It is usually used to place an image behind the text, and in the background of ALL pages in the section.
What should work is:
Hover the pointer near the top left (or bottom left) of the page to show the Header (or Footer) boxes.
Click in one the leftmost of the three boxes to place the insertion point in that box.
If a balloon pops up with "Insert Page Number" written on it, click the balloon.
If not, with the insertion point inside the box, go to the Insert Menu, and choose Page Number.
The page number should appear in the box, and in the box in the same position on every page in the document or in the section).
If this does not produce the expected result, describe in detail each action you took, and the result you saw after completing each action.
Regards,
Barry