A – all your Office documents are now the same size and appear empty when opened. Sounds like a virus.
B – Have no backup.
C – How to recover (very unlikely)
Turn off the computer! Disconnect any network cables and if using wireless besure to diable when you reboot.
Using a LiveCD (Trinity or UBCD4Win) boot the system, clear the virus and/or worm and copy any remaining documents to CD or tape. When you have cleared the virus then you can restart normally and reconnect to the network.
IF you are unable to ‘clean’ the virus – erase the hard drive and reinstall the OS (Microsoft’s current recommendation).
The reason I said recovery of your documents is unlikely, is because the truncation in size implies they were re-written. UBCD4Win includes a deleted file recovery program. And if you have the patience of Job you can use a sector editor on the disk to capture file fragments.