A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
Here's one fairly simple way that OneNote could implement this:
Add a new "View" to OneNote which is a read-only view. When this view is selected, then the UI works exactly the same as normal except that keyboard input that would change the document doesn't have any effect. This could also be a toggle on the "Home" pane. This would remove the need to deal with document permissions, require very little change to the app, and be fairly clear from a usability standpoint.