See if Page numbering /header / footer problems Word 2007 - 2016 helps.

Page numbers are usually in the header or footer of a document. This can make things confusing because any document can have numerous headers and footers.

A page number is a field. If you are in the header and type the word "page" without quotation marks, select it, press Ctrl+F9 and then F9, you will have created a page number field. If you press Alt+Shift+P you will create a page number field.

For more on page numbers, see Page Numbers in Word 2007-2016.