using (System.IO.StreamWriter sw = System.IO.File.CreateText(path)) 
{
sw.WriteLine("Hello");
sw.WriteLine("And");
sw.WriteLine("Welcome");
sw.Close(); sw.Dispose();
}

[DllImport("MY.dll")]

Assembly SampleAssembly;
SampleAssembly = Assembly.LoadFrom("c:\\Sample.Assembly.dll");
// Obtain a reference to a method known to exist in assembly.
MethodInfo Method = SampleAssembly.GetTypes()[0].GetMethod("Method1");
// Obtain a reference to the parameters collection of the MethodInfo instance.
ParameterInfo[] Params = Method.GetParameters();
// Display information about method parameters.
// Param = sParam1
//   Type = System.String
//   Position = 0
//   Optional=False
foreach (ParameterInfo Param in Params)
{
    Console.WriteLine("Param=" + Param.Name.ToString());
    Console.WriteLine("  Type=" + Param.ParameterType.ToString());
    Console.WriteLine("  Position=" + Param.Position.ToString());
    Console.WriteLine("  Optional=" + Param.IsOptional.ToString());
}

Assembly assem;
assem = Assembly.LoadFrom("c:\\NetDLL\\ClassLibrary.dll");
Object Cl1 = assem.CreateInstance("ClassLibrary.Class1");
Type t = assem.GetType("ClassLibrary.Class1");
MethodInfo add = t.GetMethod("Add");
Object[] param = new Object[2];
param[0] = 4.55;
param[1] = 3.14;
Console.WriteLine(add.Invoke(Cl1, param));

System.Reflection.Assembly assem;
assem = System.Reflectiion.Assembly.LoadFrom("c:\\NetDLL\\ClassLibrary.dll");
//Далее в этом стиле