Look, you don’t want to get into trouble later for using someone else’s material. It’s clear that the site admins don’t want it to be used elsewhere, since they have put protection in place. But of course, that’s your decision. Technically, you could use a web page text downloader like this one: https://pr-cy.io/page-to-text/ . Then you can process the text however you like. In my opinion, though, it’s better to contact the admins and ask for permission to use the lectures in your own work.