minecraft-assets/assets/minecraft/recipes/book.json

{
  "type": "crafting_shapeless",
  "ingredients": [
    {
      "item": "minecraft:paper",
      "data": 0
    },
	{
      "item": "minecraft:paper",
      "data": 0
    },
	{
      "item": "minecraft:paper",
      "data": 0
    },
    {
      "item": "minecraft:leather",
      "data": 0
    }
  ],
  "result": {
    "item": "minecraft:book",
    "count": 1
  }
}