Silent Hill: The Novel is an official Konami-published novelization of Silent Hill, written by Sadamu Yamashita and contains illustrations by Masahiro Ito. It is available only in Japanese and some chapters were translated into English by Lady Ducky, although she seems to be taking her sweet time so it is unknown if it will actually get done.
Whether or not the novelization is canon is debatable. It is unknown if Keiichiro Toyama was involved, and if Yamashita received any official story notes from Toyama. Thus, the novelization is seen as a secondary source.
One contradiction between the novelization and game is how Jodie Mason; the novelization mentions a car crash, while the game implies a disease. The novelization also uses the Good+ ending where Cybil Bennett lives.