I own the PC version of XCOM Enemy Within and am currently considering buying the Android version of Enemy Unknown. However, I'd like to also have the new content available and therefore ask whether and how the PC version files can be used for this?
The Android operating system is different enough from Windows that simply transferring the files over won't be enough. You can't play desktop games this way. In addition the Android Xcom is probably different enough that Enemy Within is almost certainly not even compatible.
Your best bet would simply be to wait until it's released on Android.