A file with .adp extension is a Microsoft Access project file that uses OLE DB component architecture to provide a direct and efficient connection to a Microsoft SQL Server database. Such files do not contain the actual tables, database diagrams or other database elements. ADP files can be created with Access 2007 and 2010. Files created with the earlier versions of Access can also be opened Access 2007 and 2010. ADP files can be opened using Microsoft Access 365.
ADP File Format - More Information
An Access project created as ADP lets you make design changes to SQL server objects such as tables and views. It also allows to create, edit, and utilize SQL features such as database diagrams, stored procedures, and user-defined function. This gives advantage over linking to a SQL server database where you cannot make changes to design and can only link to SQL server tables and views.
Data Types and Diagram Support
Date/Time Data Types
The following new date/time data types are supported in Access 2010.
Variable-Length Data Types
The following variable-length data types can be used in Access 2010 projects: