How do I get the MS Word custom dictionary (cusctom.dic) to work?

I've edited the custom dictionary in the Word Tools - Options - Spelling and Grammar tab and added the word HDA. Word still changes HDA to HAD.How do I get the MS Word custom dictionary (cusctom.dic) to work?
There is an autocorrect thing on in the Tools Drop Down menu. It has an autocorrect that changed HDA to HAD. Simply go into the AutoCorrect thing and remove the autocorrect for the specified word. This doesn't have anything to do with the Custom Dictionary, as all that does it tell you when a word is spelled wrong, and gives you close suggestions.