Use digital art software like Adobe Photoshop or Clip Studio Paint. For 3D assets, Blender could be useful.
Official BFDI assets, including Book’s, were primarily created in (formerly Flash). A complete "Book asset" package typically includes: The Body: A teal/green hardcover rectangular shape. Limbs: Thin, black stick-style arms and legs. bfdi book asset
When Book first appeared (originally known as "Dictionary"), her asset was relatively flat. The shading was simple, and the lines were slightly thicker. The text on her cover was less refined. She looked very much like a static object brought to life. Use digital art software like Adobe Photoshop or