Book

According to the Tenth Doctor, books were the best weapons in the world. They could be handwritten or printed on sheets of paper made from wood (or a similar material) that were bound together. (TV: Human Nature, Silence in the Library / Forest of the Dead)

Some books were in electronic devices, like The I-Spyder Book of Earth Creatures. (PROSE: The Last Dodo) Thinking books were books that could be read by thought processes. (PROSE: Phoenix)

Books could cover any topic and be intended for entertainment, record keeping, teaching, or other purposes. Some books were arranged in chapters, which could have titles listed near the front of the book. Some books had afterwards, text written after the main story was concluded. (TV: The Angels Take Manhattan) Some books had date of publication information. Books could be reprinted, and editions of some books were printed as late as the year 5000000000. (TV: The Unicorn and the Wasp)

Books were commonly, but not exclusively, stored in a library.

Books in the TARDIS library
The Doctor appears to be fond of reading. In addition to his quote above, he has been found reading or shown to be a fan of certain Earth authors in several incarnations. (TV: Doctor Who, The Unquiet Dead, Tooth and Claw, The Angels Take Manhattan)

The Tenth Doctor, while hiding in a library from a lupine wavelength haemovariform, called books the "Best weapons in the world." (TV: Tooth and Claw)

The Book of the Still was a book used as a rescue device for stranded time-travelers. (PROSE: The Book of the Still)

Artie Maitland was reading a book called Summer Falls by Amelia Williams. Clara Oswald said she'd read it, too, and chapter 11 was the best. (TV: The Bells of Saint John)