Format Page Numbering in Word Footer

In an eight page document in Word, my assistant created a footer and formatted the page number to look like 1 of 8, 2 of 8 etc. All is well until we close and re-open the document. Then it says 1 of 1, 2 of 1, 3 of 1, etc. 3 or 4 seasoned Word users have not been able to solve this. Is there some kind of formatting that we need to look for to overcome this? A code or something?