To clear recent documents list in Office program:
Steps:
1. In Office program, Microsoft > [program_name] options > Advanced tab > Scroll down to Display section > set the value for 'Show this number of Recent Documents:' to 0 (zero).
Where [program_name] can be Word, Excel, PowerPoint etc.
2. Click Ok
3. Repeat step 1, and set back the value for the number of Recent Documents to show to its original default, ie: 17.
Note: If you don't want this Office 2007 application to remember any Recent Documents, you can leave the value at 0 and skip this step 3.
To clear recent documents list using registry:
Eg: on Word 2007
Steps:
1. Run regedit
On window Start > Run... > type 'regedit'
2. In registry editor, goto:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Word\File MRU
3. Delete some or all of the listed items on the right frame, and restart Word 2007
Note: This works with all Office applications, not just Word, simply navigate to the appropriate registry entry.
For further information, see here.
