For example, there is an ID field where the User needs to input his/her ID number, and I want that ID number to appear in the footer?
If there is already a header or footer text in the document (for example, a side header or chapter title) and you want to add page numbers, you need to use express blocks with field codes. If you try to add page numbers to an existing footer using the Page Number button on the Insert tab, the existing text will be replaced with page numbers.