A BK file contains a book created with Adobe FrameMaker, a program used to author, enrich, manage, and publish technical documentation. It contains pages that are formatted for print and may include text as well as raster and bitmap images. BK files were replaced with .BOOK files by FrameMaker.

You most likely will only encounter BK book files if you use early versions of Adobe FrameMaker to compose technical documents. The purpose of BK book files is to organize multiple pages (stored in .FM files) into one composition, much like a real-life book. While books are an important aspect of FrameMaker, BK files are no longer commonly used by the software for saving books. In the mid-1990s, FrameMaker began saving books in version 5 with the .book file extension instead of the .bk file extension. NOTE: Since the BK format is old and deprecated you should save your books in FrameMaker as BOOK files instead of BK files.