Right now, you're creating an instance of every type defined in the assembly. You only need to create a single instance of Class1
in order to call the method:
class Program
{
static void Main(string[] args)
{
var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");
var theType = DLL.GetType("DLL.Class1");
var c = Activator.CreateInstance(theType);
var method = theType.GetMethod("Output");
method.Invoke(c, new object[]{@"Hello"});
Console.ReadLine();
}
}