Many wizards maintain that magic and writing share a common root. You don’t know about that, but you guess magic must have been involved somehow for a humble book like yourself gaining both sentience and the ability to assume humanoid shape.
Ability Score Increase. Your Intelligence score increases by 2, and one other ability score of your choice increases by 1.
Age. While books do visibly age, they can survive for many centuries or even millenia.
Alignment. Books can be of any alignment, but have a slight tendency toward lawfulness.
Size. In humanoid shape, your size is medium. As a book, you are tiny.
Speed. Your base walking speed is 30 feet. In book shape, you are immobile.
Alternate Shape. You have two shapes. Your natural shape is that of a book. Your alternate shape is that of a humanoid with one or more features reminiscient of your nature, such as ink blank eyes, permanently stained fingers, a papery texture to your skin, or similar. You can transform from one shape into the other at will as a standard action, equipment other than non-magical clothing does not transform with you. There must be enough space available for your humanoid shape for you to transform from book shape to humanoid shape. While awake and in book shape, you have access to all of your senses but you cannot move, attack, speak or take any other action that would require a humanoid body. You can only sleep in book shape.
Note that you cannot change your appearance either as a book or as a humanoid without the use of further shape changing or illusory magic.
Of the Written Word. You can cast the identify spell once per long rest and without expending material components. However, it only works on magical texts. Intelligence is your spellcasting ability for this spell.
Well of Knowledge. You have proficiency with all Intelligence skills.
Languages. You can speak Common and one other language of your choice. You also can read and write all languages. At will, you can make writing appear on yourself. This works both in humanoid and book shape.
Image: The Librarian by Giuseppe Arcimboldo (1527–1593).