string strPass = @"D:\WinAutoTest\sanjiao.exe";
            Assembly assebly = Assembly.LoadFrom(strPass);

            Module module = assebly.ManifestModule;
            Type[] types = module.GetTypes();

            Type tpForm = typeof(Form);

            foreach (Type type in types)
            {
                if (type.IsSubclassOf(tpForm))
                {                  
                    MessageBox.Show(type.FullName);
                }
            }