It is indeed unlikely to be a legal copy.
There are grey zones in copyright, and this downloadable file transgresses one of those.
I can legally scan the ABoK for my own use, but I must not distribute any such copy to anyone. I may however in a limited number use an excerpt of the book in class.
The state of the law on copying now is that one may not use an illegal copy of any work, although one legally can make a copy of some work that is available (not necessarily owned). So although I may freely copy my own ABoK for my own use, even though I own a legal copy of the ABoK, I am not allowed to dl a scan of the same book that someone else made. Analogously, for any musical performance where I own a legal copy, I may copy it to my preferred medium and use it, in the instance of a recording, I may even give copies away to friends, but even though I own a legal copy, I must not dl a copy that someone else made from the web. (And friends that recived a copy are not entitled to make second generation copies to give away, only first generation copies are allowed.)
So, regardless of the copyright notice in the book, I have certain rights to use the book; i.e. my usage is analogous to reading it, but such copies that are made therefore, must not be distributed. Anyone in possession of the book may however do the same, copy it and read it from the copy.
Of course the law issues are different in different countries, and they also may change with time. What's allowed or disallowed presently may be reversed at another time. But it is indeed interesting, that copyright notices in intellectual work in some instances are not valid, while copyright law in its national application (n.b. in Sweden it is not "copyright" as in US law) will always apply according to the Bern convention, whether there is a wtitten notice/branding claiming copyright or not.
And I think it is important to know that any intellectual work is covered by copyright, whether mentioned or not. It applies also to the USA, as signer of the Bern convention. This has to be born in mind where there is not any (c) sign on or within the work. In different countries, different rules apply to copying for private use, and these may also change with time. It has been implied in a court here in Sweden recently, that even pointing to a source of a pirated copy may be a violation, but the issue is under dispute, and the final word is still not said.
postedit: I would argue, that getting someone else's copy, when I own a legal copy, should not be punishable. After all, I did buy my right to use it. However, it is not allowed.
As law is not the same everywhere, there is a possibility that the copy is hosted somewhere where it is not illegal, but then the site may become blocked for legal reasons in most countries that subscribe to the Bern convention, and downloading from it may still be illegal.
