4 She gave me a book, ... and I read it. but I'd read it.

4. She gave me a book, ...

and I read it.

This implies a sequence of events: first she gave me a book, and then I read it. The reading happened after receiving the book.

but I'd read it.

This implies that I had already read the book before she gave it to me. The 'but' suggests a contrast or an unexpected situation.