You're allowed to physically do whatever you want to the copy of a book you've purchased. You can fold it, you can tear it, you can burn it. Hell, you can even eat it if you really want.
I can also scan the pages and print them into a new softback. I can even just retype the story and print it into a new softback.
(The quote is from the parent's comment, not the one I directly replied to but my reply fits here better.) This is not permissible under copyright law, and never has been. That would be creating a new copy, which is exactly what copyright law was created to prevent.
My understanding is that this is entirely legal as long as you don't sell the copy. Borrowing/giving it away would likely be illegal but not worth prosecuting. But a copy solely as a personal backup is allowed. We do that with data all the time.
(More generally, there are already lots of products that “covert” a book to a similar but more useful item: bookmarks, stands that hold it open, etc.)
Publishers may not like that product, and may even embargo dealers that sell them, but it’s not clear that they would have any kind of legal right to stop them, even if they were only used for this one purpose.