I know there are a lot of weird things in legal documents that aren’t actually enforceable. It’s one of the reasons every contract has a part that says invalidation of one part of this contract doesn’t invalidate the whole contract. But this one makes 0 sense to me for eBooks: “You may not:copy or burn the book or extract to a device whose principal function is to act as a storage device, for example, a CD/DVD or USB stick;”