A family of Microsoft word processing software products for creating web, email, and print documents.
You can't do it that way. Yes, the "format page number" dialog changes the one-and-only number on the page, and that affects both the header and the footer.
What you need to do is change the field that displays a number. The field code that results in the page's real number is {PAGE} (you can see this if you right-click the number and click Toggle Field Codes). In the footer (but not the header), select the page number and press Ctrl+F9 to insert another pair of field braces around it. Then type an equal sign between the left brace and the page number, and type +1 between the page number and the right brace. It should look like this:
{ = 1 + 1 }
or, if you toggle all the field codes,
{ = { PAGE } + 1 }
Finally, press F9 to update the field. In each page's footer, it will display the number one greater than the page it's on.
There's still a problem, though, because the footer of the last page will display a nonexistent page number. To fix that, you need even more stuff in the footer's field code:
{ IF { PAGE } < { NUMPAGES } { = { PAGE } + 1 } "" }
Each pair of field braces must be inserted by pressing Ctrl+F9; if you just type them on the keyboard, they won't work.