That's a bit of a discussion....
It looks like people can even save the content as PDF file (if you selected the option).
As a test I would go as admin in the courses (or platform it doesn't really matter).
Or you can see "Documents" with an open eye; click on it, it'll close the eye (make "Documents" unvisible), or in admin you uncheck the box "Documents" that allows students to browse the content.
Please let us know whether it's OK