Sure, though it's not my info, but from a message posted by an msce:

http://www.mcse.ms/archive81-2005-5-1633597.html

The .tuf file is the Transaction Undo File, and is created when performing log shipping to a server in Standby mode. From our friend, the msce:

In the standby mode, database recovery is done when the log is

restored and this mode also creates a file with the extension .TUF

(which is the transaction Undo file on the destination server). In

this mode we will be able to access the databases.