Adobe officially retired the activation servers for CS3 (which includes Audition 3) years ago. While they briefly provided a serial-free version for existing customers, most "portable" versions circulating on third-party blogs or forums are unofficial repackages. These files are common vectors for malware.
Audio technology has moved on since 2007. adobe audition 3 portable
The redesigned interface supported unlimited tracks and up to 80 inputs, making it a favorite for radio production and podcasting. Adobe officially retired the activation servers for CS3