The objects, properties, and methods exposed by Automation objects are contained in a type library. A type library is a file or part of a file that describes the type of one or more objects.
Type libraries do not store objects; they store information. By accessing a type library, applications and browsers can determine the characteristics of an object, such as the interfaces supported by the object and the names and addresses of the members of each interface.
Before you can use the Automation object exposed by an application, you must reference its type library. The reference is automatically set in the VBA IDE. For other interactive development environments you must create a reference to the AutoCAD type library file, acax17enu.tlb, which is located at c:\program files\common files\autodesk shared. To access Sheet Set Manager objects in the VBA IDE or in other environments, you must create a reference to the AcSmComponents17 1.0 type library file, AcSmComponents17.tlb, which is located at c:\program files\common files\autodesk shared.
You can use an application's objects without referencing the application's type library. However, it is preferable to add the type library reference for the following reasons: