Invert a text file - Tutorial C# Sharp

using System;
using System.IO;
namespace InvertText
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Enter name file: ");
            string fileName = Console.ReadLine();

            if (File.Exists(fileName))
            {
                StreamReader myfileRd = File.OpenText(fileName);
                string line;
                int countLines = 0;

                // Count lines of file
                do
                {
                    line = myfileRd.ReadLine();
                    if (line != null)
                        countLines++;
                }
                while (line != null);
                myfileRd.Close();

                // Write of array of lines
                string[] lines = new string[countLines];
                int countLine = 0;
                myfileRd = File.OpenText(fileName);
                line = "";
                do
                {
                    line = myfileRd.ReadLine();
                    if (line != null)
                    {
                        lines[countLine] = line;
                        countLine++;
                    }
                }
                while (line != null);
                myfileRd.Close();

                // Write of file
                StreamWriter myfileWr = File.CreateText(fileName + ".tnv");

                for (int i = lines.Length - 1; i > 0; i--)
                    myfileWr.WriteLine(lines[i]);

                myfileWr.Close();

            }
            else
                Console.WriteLine("The file no exists.");
        }
    }
}