 <p>I solve the problem with this code.and we shold to use interface "IPlugin" in a seperate class library and use in other project.</p> <pre><code> Assembly objAssembly = Assembly.LoadFrom("Company.dll"); Type objAssemblyType = objAssembly.GetType(); foreach (Type type in objAssembly.GetTypes()) { if (type.IsClass == true) { var classInstance = objAssembly.CreateInstance(type.ToString()) as IPlugin; lblFullName.Text = classInstance.FullName("Mr. "); } } </code></pre>