In the Registry Editor, have you located the HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Word\Reading Locations key? You'll find the subkeys in the pane on the left.
To set permissions on the key mentioned above, right-click and choose Permissions on the context menu. The exact steps depend on your version of Windows. It may not even be possible to set permissions with all versions of Windows.
Changing anything under HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Word\Reading Locations only affects the user currently logged in to the computer. You will have to locate the corresponding key for each user account: HKEY_USERS\User_Name_Here\Software\Microsoft\Office\15.0\Word\Reading
Locations. For more on the registry, you should post in the Windows forum. See http://answers.microsoft.com/en-us/windows/forum?tab=QnA&status=all&mod=&modAge=&advFil=&postedAfter=&postedBefore=&tm=1377454747776.