A family of Microsoft word processing software products for creating web, email, and print documents.
First you might want to review this article: https://support.office.com/en-us/article/Add-page-numbers-to-a-header-or-footer-46d6dfe5-f99b-40d8-8809-be4808a291f4
Then you might want to confirm that you don't have "Different Odd & Even Pages" checked.