Adobe Reader X displays recently accessed documents as part of the File menu.
If you want to clear the recently accessed documents in Adobe Reader, then you can use the Preferences settings to change this behaviour. In Adobe Reader, click Edit menu and select Preferences from the menu list
In the Preferences screen, navigate to document categories and then the Open settings section.
To clear the recently accessed document, set the value as zero for Documents in recently used list. Click OK button to apply and save the changes.