What's the legal status of this? I'm fairly confidently betting "illegal" since the Princeton University Press's own page about the book offers an ebook versio

What's the legal status of this? I'm fairly confidently betting "illegal" since the Princeton University Press's own page about the book offers an ebook version for sale at a nontrivial price, which I doubt they would be doing if they were also offering a free PDF download. (My saying this is not intended to imply anything about the ethics of reading this copy online, or downloading it, or printing it out, or of Doron Zeilberger's decision to make it available. Or for that matter about the ethics of selling it commercially and not making it officially available for free. Whatever the rights and wrongs, some people will care whether it's legal or not, and I'm pretty sure it's not.)