A book file is a collection of documents that can share styles, swatches, master pages, and other items. You can sequentially number pages in booked documents, print selected documents in a book, or export them to PDF. One document can belong to multiple book files.

One of the documents added to a book file is the style source. By default, the style source is the first document in the book, but you can select a new style source at any time. When you synchronize documents in a book, the specified styles and swatches from the style source replace those in other booked documents.