Written Books are an item in Minecraft. These items are only obtainable in the game by "publishing" a Book and Quill.
When playing in pure Vanilla Minecraft, with no mods or plugins, after a book has been signed an closed you will not be able to edit it again.
Librarian Villagers will trade The Player for a Written Book, regardless of what writing is inside of it.
They have the gleam of an Enchanted Item or the Nether Star, but they are not enchanted.
After writing in a book, pressing Esc instead of the Done button will not save your changes.