I don't know about pdfs.
TWD Chronicles is good. It's the official companion book of season 1 and issues #1-84. Good info about Frank Darabont turning the comic book into a show. He's the guy who made movies of Stephen King's Shawshank Redemption, The Green Mile, and The Mist.
Also the (unauthorized) Triumph of the Walking Dead, that talks about the success of the show and comic book, in the form of essays written by different people, one of which is Jay Bonansinga who co-wrote the novels with Kirkman.
"This is my book, take a look, see if it grabs your attention, with a hook, the queen took the rook, into a new dimension" Tajeco