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.ADI File Extension

File Type 1	AutoCAD Device-Independent Binary Plotter File (Most common)
File Format	File
Common?	No
File Description	Black and white bitmap generated by AutoCAD
Program(s) that open adi files	Windows: Autodesk AutoCAD

File Type 2	Dynamics AX Developer Documentation Index File
File Format	Proprietary File
Common?	No
File Description	Contains an index of developer documentation (.ADD) files used by Microsoft Dynamics AX software; provides quicker access and search capabilities for the help documentation.
Program(s) that open adi files	Windows: Microsoft Dynamics AX

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/adi