FileInfo.com - The File Extensions Resource

.ADD File Extension

File Type	Dynamics AX Developer Documentation File
File Format	File
Common?	No
File Description	Application developer documentation data file used by Microsoft Dynamics AX, a business management application; contains development help documentation for using the program; arranged by language.
Program(s) that open add files	Windows: Microsoft Dynamics AX

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