MS Office programs will track their own Recent Files list to make it easier for users to remember the last file they were editing.
NTUSER.DAT\Software\Microsoft\Office\VERSION
* 14.0 = Office 2010 * 11.0 = Office 2003
* 12.0 = Office 2007 * 10.0 = Office XP
NTUSER.DAT\Software\Microsoft\Office\VERSION\UserMRU\LiveID_####\FileMRU
* 15.0 = Office 365
Similar to the Recent Files, this will track the last files that were opened by each MS Office application. The last entry added, per the MRU, will be the time the last file was opened by a specific MS Office application.