What you are talking about is the footer. (This is the bottom half of a header/footer pair.)

If what you want in the footer also appears in the body of the document on that page, the simplest way to incorporate it in a header or footer is the StyleRef Field.

Each Word Section has three headers and three footers which are independent of one another and which may or may not be displayed depending on which options you have chosen. Sections / Headers and Footers in Microsoft Word 2007-2013

If you can, use the StyleRef field instead of changing the footer.
Header/Footer Settings Recap