The way to change traditional Chinese characters into simplified Chinese characters in book app is to enter the reading interface, bring up the reading menu, find the font settings, and check the check box for reading traditional Chinese characters.

Traditional Chinese characters, a font form of Chinese characters, are called "traditional Chinese characters" in Europe and America. Generally speaking, it refers to the Chinese characters replaced by simplified characters in the Chinese character simplification movement, and sometimes it refers to the whole Chinese character regular script and official script writing system before the Chinese character simplification movement.