Until such time as Adobe respond to the hundreds of requests they have had for an option in Acrobat X (Windows version) to remove the annoying "Welcome Screen" (don't hold your breath!) many people will continue to be annoyed by it, and especially by the clumsily-implemented "recent files" list (which does not detect when those files have been deleted/moved, and is something of a security concern in many environments).
Here is a way to keep the "Recent Files" list empty, permanently...
Open Regedit and go to HKEY_CURRENT_USER\Software\Adobe\Adobe Acrobat\10.0\AVGeneral\cRecentFiles
-Delete all values contained in the cRecentFiles key (all the entries in the right-hand pane)
-Right-click cRecentFiles and choose Permissions.
-Uncheck â€œInclude inheritable permissionsâ€¦.â€
-It will ask you if you want to Add the permissions inherited or Remove them. Choose Remove, then Ok.
Acrobat will now be unable to write anything to this registry key - hence the "recent files" list will remain empty.