The .bak file often is a renamed copy of a SQLite database ( shifenzheng.db ) or Microsoft Access .mdb file. The software renames it to .bak to prevent accidental overwriting or opening by users.
If the file is orphaned (no associated software) or found in an unauthorized location (e.g., a USB drive, a personal Downloads folder): shifenzheng.bak
To ensure you never create a shifenzheng.bak vulnerability: a USB drive