What is an ACCDB file? A file with .accdb extension is a Microsoft Access 2007 database file that stores users data in tables. It supports storing custom forms, SQL queries, and other data. ACCDB files replaced MDB files after Microsoft shifted to XML based file structure. ACCDB files can still be converted to MDB with old compatibility. However, the ACCDB are the widely used Access database file format now. Microsoft also supported additional features in ACCDB format such as possibility of s...