You can accomplish this format by adding a format switch to the page field.

{ PAGE \# "000" }

To show/hide field codes, press Alt+F9. After you have edited the code, press F9 to update.

But note that these changes will not reflect in the table of contents, a list of figures, or in cross-references. These references all make use of the page number format as specified in the Page Number Format dialog box.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional