using System;

​

public static class DateTimeExtensions

{

    public static string ToCFDIFormat(this DateTime dt)

    {

        return dt.ToString(@"yyyy-MM-dd\THH:mm:ss");

    }

}

​

public class Program

{   

    public static void Main()

    {

        Console.WriteLine("Fecha: " + DateTime.Now.ToCFDIFormat());

    }

}