Now available in beta, the 1Z1-060 exam, this gives access to 12c from OCP 9i, 10g or 11g. More information is available here.
If you do not own the OCP, you must first get 12c OCA certification. In this case it is necessary to pass 1Z0-061, 1Z0-062 and 1Z0-063 exams.
Here you can download database engine (Release 18.104.22.168.0)
In this link is the documentation