Both Word 2013/2016 and Word Online have the capability to add page numbers to headers, footers, or margins of documents.

The easiest way to access this is to:

1. Click the Insert tab in the ribbon.
2. Click the Page Number icon in the Header & Footer section, and select Top of Page, Bottom of Page, Page Margins, or Current Position, depending on where you want your page numbers to appear.
3. Optionally, if you’d like your numbers to appear in a different format, or if you need to control where numbering starts, click Format Page Numbers.

For a visual demonstration in both Word 2013/2016 and Word Online, check out the video above.