Probably you are looking for JavaScript™ for Acrobat® API Reference.
This reference should be the most complete. But, as @Orbling said, not all PDF viewers might support all of the API.
EDIT:
It turns out there are newer versions of the reference in Acrobat SDK (thanks to @jss).
Acrobat Developer Center contains links to different versions of documentation. Current version of JavaScript reference from Acrobat DC SDK is available there too.