Remarks
Extension DLLs use the macro AFX_EXT_CLASS to export classes; the executables that link to the extension DLL use the macro to import classes. With the AFX_EXT_CLASS macro, the same header file(s) used to build the extension DLL can be used with the executables that link to the DLL.
In the header file for your DLL, add the AFX_EXT_CLASS keyword to the declaration of your class as follows:
class AFX_EXT_CLASS CMyClass : public CDocument
{
// <body of class>
};
For more information, see Export and Import Using AFX_EXT_CLASS.