Has anyone read the book?

I have. It's good, but not he best of the series. Good luck finding it, I've found it to be kind of rare. You may find some of the others in the Parker series. Feel free to pick them up it doesn't make to big a difference if you read them out of order.
I hope you start reading this series, it quickly became one of my favourites.

Edit - The first book has three different titles "the Hunter" "Point Blank" and "Payback"

I've come at this in the opposite way to you. I've read the book, and plenty more of the 'Parker' series (Donald E Westlake writing as Richard Stark). I then discovered there was a movie or two made. Point Blank is a good movie and as brilliant as Marvin is in the role of Walker (Parker) he can't, maybe no one can, portray the cold, silent, self-serving menace that is the Parker villain. Mel Gibson tried (badly) a few years back but he made the fatal flaw of thinking a 5'8" actor could pull it off.
The Parker novels are clinical crime capers mostly centred on Parker's dealings with inept and greedy third parties on the various heists he finds himself a part of (not all involving the mob). I highly recommend them as uncomplicated crime reading and whilst you don't need to read them in sequence, there are a few threads that pass nicely from novel to novel.
Trivia: The George Stark villain in Stephen King's 'The Dark Half' is partly based on Parker.

Yes, I've just finished the book, which I read because I knew the film was based on it. Was the book any good? Not as good as the film, but then, it wasn't very similar to the film at all. The revenge motif was there, but in the book, the main character was a cold-blooded killer (whereas Walker doesn't actually kill anyone at all in the film). The book also didn't have the different levels of meaning that the film had - it was just a straight gangster tale, with none of the metaphysical elements of the film - there's no doubt that Parker (Walker's name in the book) is alive - the story isn't a revenge fantasy and Walker isn't a ghost, either - there's no depth to the book at all. However, to be fair to both, they are different animals. The book sets out to be a straight crime thriller and succeeds in doing so (although I have to say I've read better), but the film is attempting considerably more than that.