I need to import a WAV file into a CAP 9 Software Simulation Project

You can drag it into the Library panel (from Finder or Explorer).

There is an Import button as well

Audio will automatically end up in the Audio folder.

You can then drag the file onto the slide where you want that audio, it will be slide audio. Or you can use the audio as object audio (attached to an object) or triggered with the command Play Audio.

You can also import Audio directly to a slide as Slide audio using:

Media button, Audio

Audio menu, Import to Slide

Wav-file is fine, when published it will be converted to MP3 by Captivate to reduce the size.