There are ways to make it more difficult to copy or extract content from web pages. Normally, documents; HTML, PDF, MS Office, text files, images, etc.; are downloaded by the browser into its cache in order to display them to the user. All the user has to do is save the files from the browser cache.
However, any clever bunnies who know about serialised data would know how to capture the stream in their browsers, using freely available developer tools, deserialise it, and save it as files. This is how a lot of video download browser plugins work. Still, most regular learners don't know how to do that.
Also, I wonder if it's possible to capture the print screen command and return a blank page? Anyone ever done that?