What you need to insert is a field which has that text. A field is a command which Word can execute. You may be familiar with automatically-updating date fields, for instance.

For your purposes, the easiest way to do this is to place your cursor where you want the name to be in your footer and press Ctrl+F9 (the F9 key above the regular keys). This will insert a field in the form of a pair of curly brackets with two spaces between them,and your cursor will be between the spaces. Simply type the FILENAME \p (or, if you have already copied it to your clipboard, paste it in). Do not remove the spaces between your text and the brackets and do not add any. Then, move your cursor outside of the brackets and press Alt+F9. The result of the field, your file name path, will appear. Pressing Alt+F9 wil toggle between the two.

Does this resolve your problem?