Nothing on my Ubuntu 11 system seems to automatically open rtfd files.
As far as I know, it is a mac file and it can't be opened in Linux.
See also in Wikipedia.
While there might not be any GNU/Linux applications that support
See this Wikipedia article for more information about the RTFD format.
Also, that article suggests that Ink.app, and possibly other GNUstep programs, can open RTFD files; it should be possible to install that in Ubuntu, though I don't think there's any official Ubuntu package that provides it.