Let's say there is a copyrighted book which is published illegally by someone. Is it also illegal for the people who have received the book to read it?
Copyright law regulates copying of protected material. In the US, there are no laws that specifically prohibit reading anything. It may be illegal to be in possession of something (classified material), but if it is legal to be in possession, it is legal to read. (Do not confuse "read" with "read aloud to an audience" a.k.a. perform, which is a separate copyright protection). It is not illegal to be in possession of material that was copied without permission.