PDG is a digital book format similar in structure and functionality to PDF. PDG files are used to store e-books. They are popular in Asia, mainly in China. PDG files were handled by an e-book reader called SSreader. These files were available in the Superstar Digital Library service and the twin Chinamaxx. These are electronic libraries with over 700,000 Chinese books published after 1949 in 22 categories.

Currently, the PDG format is rarely used and is considered obsolete.