using System;

​

​

public class SuperClass

{

    public string GetDocument()

    {

        return "ValidDocument";

    }

}

​

public class SubClass : SuperClass

{

    public new string GetDocument()

    {

        return "Invalid document";

    }

}

​

public class Program

{

    public static void DoSomething(SuperClass superClass)

    {

        var document = superClass.GetDocument();

        Console.WriteLine(document);

    }

    public static void Main()

    {

        var b = new SubClass();

        DoSomething(b);

    }

}