I am creating a document where I say, for example, see page 120 for more details.
As I add or delete pages, is there a way for the document to automatically change the text (the 120) to reflect the new page number.
You can update all the fields by pressing Cntrl A to select all your text and then F9 to update all the cross-reference fields. If you want to do them one at a time, select the cross-reference text, right click and select Update Field. Also if you have the option "Update fields before printing" selected in the Display tab of Word Options, switching to Print Preview will also update the fields. That's as automatic as it gets.