The type of digital document format commonly used for e-books is EPUB (Electronic Publication). EPUB is a widely adopted open standard that allows for reflowable content, making it adaptable to various screen sizes and devices. This format supports rich media features, including images, audio, and video, enhancing the reading experience. Additionally, EPUB files can incorporate elements like fonts and styles, ensuring consistent formatting across different e-readers and applications, making it a popular choice among authors and publishers for distributing digital literature.