Adobe Reader XI allows you to reduce the list of recently used documents displayed when you open the application, but you cannot delete this list directly. However, by deleting the Windows registry keys associated with the entries on the list you can clear the entire list safely. As this must be done every time you want to delete the Most Recently Used list, it might be practical to deny Adobe Reader access to this registry key completely and thus prevent the list from being created at all.
Delete the Most Recently Used List
The contents of the Adobe Reader Most Recently Used list is stored under the "cRecentFiles" key in the Windows registry. Access this key by opening "HKEY_CURRENT_USER | Software | Adobe | Acrobat Reader | 11.0 | AVGenera" and then deleting the files listed below the "cRecentFiles" key. You can also delete the "cRecentFiles" key itself instead of deleting the individual sub-keys as Adobe Reader recreates the key automatically when opened.
Permanently Delete the Most Recently Used List
To permanently get rid of the Most Recently Used list in Adobe Reader, right-click the "cRecentFiles" registry key in Regeditor and select "Permissions." Select "Advanced" and then clear the "Include inheritable permissions from this object's parent" check box. Select "Remove" and then select "Apply" to make the change. By not allowing Adobe to access this registry key you won't have to use Regeditor every time to clear the most recently used list, as there will be no list.