Currently Adobe Acrobat Reader for Linux is at version 9.5.5. Does anybody know when Adobe is going to release a version 10 or 11 and have the ability to use a Reader Extension enabled PDF file?
Never would be the safest guess. Their Linux support has always been terrible, and I don't ever expect that to change. I've found Adobe Acrobat Reader to be quite impressively slow and resource hungry, so finding an alternative may be in your best interest anyway. I wouldn't be surprised if they just gave up on delivering a reader for the platform.
Have you tried Okular (KDE) or Evince (Gnome)? I'm not familiar with Reader Extension enabled PDF files, but from a Google search, it appears to just enable a few useful pro features. On the first PDF form that I found (Form W-4 2014), Okular let me fill it in and run a "Save As..." to retain all my information, however the file did give me an warning/error
"This document has XFA forms, which are currently **unsupported**." Okular also supports commenting/markup, but I'm not sure about the other features.
I'm running Linux Mint 16 KDE, and don't want to install a dozen packages just to test Evince.
Update PDF Studio (paid application w/ free trial) is supposed to support static XFA forms, among many other Acrobat Pro level features. They have a Linux version and plans to support LiveCycle XFA forms in version 10 or 11 (currently on 9).