to be an open book: to be easy to understand; to have no secrets
E.g. Julie is an open book. I always know what she is going to do next.
The message of the conference call is an open book. We need to save money.
to read between the lines: to understand indirect communication; to interpret message from hints
E.g. My boss told me to take a very long vacation. Is he saying I should leave the company?
I’ve got a note from my son. He did not say anything but I could tell by reading between the lines that something is wrong.
a bookworm: One who spends much time reading or studying.
E.g. He spends all day in the library. He's a real bookworm.
When I was a child, my classmates called me a bookworm, because I was reading books in all my free time.
off the books: without being included on the official (financial) records
E.g. Waiters often work off the books, they get paid in cash.
The company was fined for paying staff off the books.
to read into: to attach or attribute a new or different meaning to something
E.g. You should not read anything else into his message. He means exactly what he says.
Sharon tends to read into everything her boyfriend says or does, and they have a lot of arguments because of this.
to read the fine print: to know all the information contained in a document
E.g. You should always read the fine print before signing a contract.
If you read the fine print, you will see that this deal is not as good as it sounds.
read up: to research information about someone or something.
E.g. The teacher told the children to go to the library and ready up on Martin Luther King, Jr.
I like to read up on the places I plan to visit before my travel.