A family of Microsoft word processing software products for creating web, email, and print documents.
The page number is a { PAGE } field. To see the field code, press Alt+F9 or Alt+Fn+F9, depending on your keyboard.
To add the page number minus 1, press Ctrl+F9 (or Ctrl+Fn+F9 on some keyboards); Word adds field delimiters, { }. Type in an equal sign. Press Alt+Shift+P to add another PAGE field. Press the SpaceBar and then a hyphen and then 1.
The screen shot below shows the field construct, with nonprinting characters displayed. (The dots represent space characters and the pilcrows, ¶, represent paragraph marks/returns.)
Select the whole field construct and press F9 (Fn+F9) to update it.
If you put the field inside the page header or footer, the field result will update automatically.