In a 500-page document any formatting should be done using styles, not direct formatting through the font menu. But that isn't the source of your problem.

Assuming your reference style is Heading 3, press Alt-F9 to display field codes. Try:

{ StyleRef "Heading 3" \*CHARFORMAT }

Make sure the field (revealed) has the character style applied you want to be using.


Understanding Styles in Microsoft Word
Why use Microsoft Word’s built-in heading styles?
Yet Another "Use Styles" Verbal Beating!

If you are using Word more than 6 hours a month you owe it to yourself to learn to use Styles in Word. Within two months you will more than have recovered any time you spend learning them. If you use Word more than that the savings are much more dramatic.



I recently had occasion to edit a 100-page document that was created without using styles. It was formatted completely with direct formatting.
Each page ended with a page break.



Each time it had to be saved, the save took more than 60 seconds, during which time Word was frozen. A similar-sized document formatted using Styles takes less than 3 seconds for me to save. This difference was due entirely to the document being directly formatted - a much higher level of complexity.



Each paragraph mark in a directly-formatted paragraph carries with it up to fifty different formatting commands. When formatted using Styles, that paragraph mark will carry with it one command - use this style!