PBK meaning in File Type ?

A telephone directory, commonly called a telephone book, telephone address book, phone book, or the white and yellow pages, is a listing of telephone subscribers in a geographical area or subscribers to services provided by the organization that publishes the directory. Its purpose is to allow the telephone number of a subscriber identified by name and address to be found.

The advent of the Internet and smartphones in the 21st century greatly reduced the need for a paper phone book. Some communities, such as Seattle and San Francisco, sought to ban their unsolicited distribution as wasteful, unwanted and harmful to the environment.

The slogan "Let Your Fingers Do the Walking" refers to use of phone books.