You could also extract the APIs archive to a place on your local disk and view them with an external browser--look for the archive in $NBHOME/docs/OpenAPIs.zip.
If you install this module, you will also get code completion on all API classes as used by the standard Editor. Note that this feature may require an IDE restart, and may not work for clients of multiuser installs (in which case you should manually copy the files system/ParserDB/OpenAPIs.jcb and system/ParserDB/OpenAPIs.jcs from the root install directory to your own).
Warning: the API documentation and code completion reflect the current development state of the Open APIs. If you are working with the API Support module in a version of the IDE earlier than the API Support was built for, you may need to restrict your usage of a few APIs to those available in your build.
Also see the NetBeans API website for update information and other information and downloads.