You can have Word calculate page numbers using the following nested field:

{ = { PAGE } - 1 }

To insert each pair of field delimiters, { }, press Ctrl+F9. Type the code as shown, and pay attention to the spaces (which may be crucial in some versions of Word). When you are done, click F9 to update. To show/hide field codes, use Alt+F9.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional