Penguin Books (in-universe)

Penguin Books (COMIC: The Train in Vain and the Junkmail Messiah) were a group which published books. (TV: Everything Changes, COMIC: The Train in Vain and the Junkmail Messiah) Their logo was a penguin standing in a yellow ellipse.

Books published by the group included The New Penguin Dictionary of Abbreviations (TV: Everything Changes) and Reginald Tyler's The True History of Planets. (COMIC: The Train in Vain and the Junkmail Messiah)

Behind the scenes
In the real world, Penguin Character Books have published several Doctor Who books.