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I can't tell you more than what I read on those pages. And what Wikipedia says.
As for the reddit comment about archive.org borrowing and possible saving that book instead just a loan: the browser cache method could work.
I have not borrowed book like this ever, so I'm not sure how it works, however I browsed a site which archives many documents and offers views. The viewer of that particular site loads pages in pdf formats, and all are cached on the hard drive by the browser, so it was a matter of going through the pages, and then copypasting the files from the cache to somewhere, then unifying them into a single pdf with a suitable program.
Protip: before browsing it is a good idea to empty the cache so only the files for that book will be in there, makes the sorting of the files easier.
You also have to find the directory for your browser's cache.