To be able to view PDF Files within BCT aClass with Adobe Reader 9 or higher, you have to register the "%BCT_EOMS_DIR%\bin\windows\acropdf_server.exe" on the clients. This is a one time registration and is not required on each start of Teamcenter/BCT aClass.
"%BCT_EOMS_DIR%\bin\windows\acropdf_server.exe" -regserver