How do you add it to the existing AFCAD?
Go to scruffyduck and download the latest version of ADEX for your chosen sim and install it. If I recall since it's been a while since I installed it, I think you need the SDK installed if your using FSX. ADEX comes with instructions on how to place objects, so just follow the instructions that come with it. For this reason, using Instant Scenery might be easier to do it but it's not free.