For those possibly confused (like me): this is not a new edition of Concrete Mathematics. It's the text of the published book, but typeset astoundingly poorly. The actual book is sublimely set, as one might expect from Knuth.
The content of the work is very difficult for me, but I think it worthwhile. I doubt it'll be that much use to a non-mathematical audience, tho.
The reason why the typeset is poor is due to the fact that all the mathematical symbols are in the "Concrete and Euler or Concrete Math", whoever published the pdf probably doesn't have that font installed. Hence the poor quality. I have yet found a version online that matches the physical book typeset quality.
It must have a different body font, too, because the tracking on page 4 (for example) is atrocious.
Is this a legally offered file?
It's been on the xpmath site since 2003. If it doesn't seem legit please feel free to suggest that this post is deleted (I'm not exactly sure if/how I can delete it myself after an hour has passed)
I can't imagine Knuth would have approved this. It looks bad - the physical book looks great. It doesn't even use the Concrete Roman typeface he designed for the book.
This PDF looks to me like a scan that was OCR'd; anything the recognizer couldn't handle was left as a bitmap.