Hi, I find that Steam version of Crimes and Punishment has a free Digital Book for downloading, which is not included in GOG version. Anyone has an idea of this? Thanks.

I remember that GOG gave this away a little while after C&P came out here except they called it a "Thank you artbook". I've checked my copy and it seems to be the same as what Steam are giving away as a free download if you have the base game. Funnily enough, like you say, there is no such download available on GOG (just checked the game library page to double check) so it may just be an oversight by GOG who have forgotten to list it . It might be worth contacting support to see what they say about it. Hope this helps.