If the issue is with your users receiving “documents FROM the internet” then chances are it is a setting with their person documents. If you are an old school Notes shop from 4.x days and keep upgrading then chances are you still have users that their “Default Format Preference for Incoming Mail” is set to: “Prefers Notes Rich Text”.
This wont’ help them for any previous documents they have recieved, but changing it to either MIME or “Keep in Senders Format” it should help them going forward.