In the standby mode, database recovery is done when the log isrestored and this mode also creates a file with the extension .TUF(which is the transaction Undo file on the destination server). Inthis mode we will be able to access the databases.
Thanks Brendt. Here is what I found
File containing information regarding any modifications that were made as part of incomplete transactions at the time the backup was performed. A transaction undo file is required if a database is loaded in read-only state. In this state, further transaction log backups may be applied.
RESTORE <database> WITH RECOVERY