This capability is part of the core product and not a separate download. It worked fine in 4.0, but I don't see it in the 4.2 documentation. That might be because there is some sort of incompatibility, but my suspicion is that the documentation just isn't up-to-date yet. It isn't very hard to try out and see:
That page is erroneously marked "Enterprise Only" (https://issues.alfresco.com/jira/browse/DOC-412). I added a comment about the missing documentation for 4.2. If you try the 4.1 instructions and it doesn't work in 4.2, then we need to get that reported as a bug. I don't see any reports about problems with Liferay integration reported against 4.2 currently.
