alt Hacker News"Test Your C Skills" is a published book by Yashavant Kanetkar, apparently published in 2005, and still available in paperback. The document you linked to appears to be a scan of a printed copy of that book, and is almost certainly in violation of copyright. The cover and the title and copyright pages are notably missing.
That's worth being aware of, though somewhere around 20 years is where I start caring a lot less about copyright from a moral or practical point of view. Yeah, that book stays out of the public domain until the next century, but it shouldn't.