Does anyone knows where to buy a pdf version ?

If you google for "Beginning Visual C++ 2008" then one of the first few links is to an ebook retailer who is selling an Adobe Digital Edition of the book.
The ebook costs about the same as the printed edition.
I don't know anything about Adobe Digital Edition.
It seems to be a DRM protected PDF but you'd need to find out more at the Adobe website: http://www.adobe.com/products/digitaleditions/#download
I assume the ebook is a legitimate product and that Wrox / Ivor Horton get royalties, etc although I don't know if that's true.
Perhaps you should talk to Wrox customer support (via email or online chat) to ask about availability of a legal PDF copy of the book.