using System;

using System.Globalization;

using System.IO;

public class Program

{

    public static void Main()

    {

        // Defining Format and Testing it via "DateTime.ToString(format)"

        string format = "MM/dd/yyyy HH:mm:ss tt"; 

        string dtNow  = DateTime.Now.ToString (format);

        Console.WriteLine ("Date Time Now : " + dtNow);

        var outfile = Path.Combine(

            "c:\\path",

            DateTime.Now.ToString("{0,4:D4}")

        );

        // 

        //DateTime.Now.ToString("OutFile_{0,4:D4}{1,2:D2}{2,2:D2}_{3,2:D2}.csv")

        Console.WriteLine("Results will be written in file {0}.", outfile);

    }

​

}