The AutoCAD .NET API is made up of different DLL files that contain a wide range of classes, structures, methods, and events that provide access to objects in a drawing file or the AutoCAD application. Each DLL file defines different namespaces which are used to organize the components of the libraries based on functionality.
Before classes, structures, methods, and events found in one of the AutoCAD .NET API related DLLs can be used, you must reference the DLL to a project. After a DLL is referenced to a project, you can utilize the namespaces and the components in the DLL file in your project.
Once a AutoCAD .NET API DLL is referenced, you must set the Copy Local property of the referenced DLL to False. The Copy Local property determines if Microsoft Visual Studio creates a copy of the referenced DLL file and places it in the same directory as the assembly file of the project when it is built. Since the referenced files already ship with AutoCAD, creating copies of referenced DLL files can cause unexpected results when you load your assembly file in AutoCAD.
The AutoCAD .NET API DLL files can be located at <drive>:\Program Files\AutoCAD 2011 or as part of the AutoCAD 2011 ObjectARX SDK which can be downloaded from http://www.objectarx.com or the Autodesk Developer Network Web site (http://www.autodesk.com/adn).