How to sort the content of file using merge sort..

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace Splitfiles
{

    public partial class Form1 : Form
    {
        public FileStream fs;
        System.IO.StreamWriter writer;

        string file_write;

        public Form1()
        {
            InitializeComponent();
        }


        //List<string> Packets = new List<string>();

        //Merge file is stored in drive
        //string SaveFileFolder = @"c:\";

        private void brows_Click(object sender, EventArgs e)
        {
            try
            {
                openFileDialog1.ShowDialog();
                txtBrowsFile.Text = openFileDialog1.FileName;

                fs = new FileStream(txtBrowsFile.Text, FileMode.Open, FileAccess.Read);
                string name = Path.GetFileName(txtBrowsFile.Text);
                //int FileLength = (int)fs.Length / 1024;

            }
            catch (Exception ex)
            {
                lblSendingResult.Text = "EXCEPTION:" + ex;
            }
        }



        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            //string fpath="E:\\one.txt";
            string name = Path.GetFileName(txtBrowsFile.Text);
            StreamReader dr = new StreamReader(Path.GetFileName(txtBrowsFile.Text));



            while (dr.Peek() != -1)
            {
                string contents = dr.ReadToEnd();
                /*string[] mer = new string[contents.Length];
                int len = contents.Length;
                int i = 0;
                for (i = 0; i < len; i++)
                {
                    mer[i] = (contents);*/


                textBox1.Text = contents;


            }

            txtBrowsFile.Clear();

        }

        private void button2_Click(object sender, EventArgs e)
        {
            //StreamWriter dw = new StreamWriter(Path.GetFileName(txtBrowsFile.Text));


        }

        private void button3_Click(object sender, EventArgs e)
        {
            string name = Path.GetFileName(txtBrowsFile.Text);
            StreamReader dr = new StreamReader(Path.GetFileName(txtBrowsFile.Text));
            string content;

            content = dr.ReadToEnd().ToString();

            textBox2.Text = textBox1.Text + (content);
            textBox1.Clear();


        }

        private void button4_Click(object sender, EventArgs e)
        {


            //string name = Path.GetFileName(txtBrowsFile.Text);
            //StreamWriter dw = new StreamWriter (Path.GetFileName(txtBrowsFile.Text),true);
            //StreamWriterfile_write = "Path.GetFileName(txtBrowsFile.Text)";
            //writer = new System.IO.StreamWriter(file_write, true);
            //dw.Write(textBox2.Text);
            //dw.Close();
            file_write = "C:\\Users\\asadali\\Documents\\file.txt";
            writer = new System.IO.StreamWriter(file_write);
            writer.Write(textBox2.Text);
            
            writer.Close();
            MessageBox.Show("wrote File");
        }

        private void button5_Click(object sender, EventArgs e)
        {
            string name = "C:\\Users\\asadali\\Documents\\file.txt";
            StreamReader dr = new StreamReader(name);
            while (dr.Peek() != -1)
            {
                string contents = dr.ReadToEnd();
                string[] mer = new string[contents.Length];
                int len = contents.Length;
                int i = 0;
                for (i = 0; i < len; i++)
                {
                    mer[i] = (contents);
                    textBox1.Text = contents;

                }
                /*   string[] arr = textBox2.Lines;
                   int i;
                   for (i = 0; i < arr.Length; i++)
                   {

                       textBox2.Text = arr[i];

                       i++;
                       arr[i] = textBox1.Text;
                   }*/

            }
            //string [] contentss = textBox2.Lines.ToArray();

            // for( int i=0;i<contentss.length;i++)>
            //{

            //string[] lines = File.ReadAllLines("C:\\Users\\asidali\\Documents\\file.txt");

            //string[] a = new string[lines.Length];
            //int i;
            //for ( i = 0; i < lines.Length; i++)
            //{
            //  lines[i] = a[i];
            //a[i] = textBox1.Text;
            //}
            //.textBox1a[i] = textBox1.Text;
        }
    }
}
            /*string name = Path.GetFileName(txtBrowsFile.Text);
            StreamReader dr = new StreamReader(Path.GetFileName(txtBrowsFile.Text));

            while (dr.Peek() != -1)
            {
                string contents = dr.ReadToEnd();
                string[] mer = new string[contents.Length];
                int len = contents.Length;
                int i = 0;
                for (i = 0; i < len; i++)
                {
                    mer[i] = (contents);


                    textBox1.Text = contents;

                }

                //string[] lines = this.textBox1.Text.Split('\n');
                //MessageBox.Show(lines.Length.ToString());

        }
    }
            /*private string[] Mergeso                                                                                                                                            rt(string[] mer)
 {
     if (mer.Length <= 1)
     {
         return mer;
     }

     int firstPart = mer.Length / 2;
     string[] strings1 = new string[firstPart];
     string[] strings2 = new string[mer.Length - firstPart];

     string[] sorted = new string[mer.Length];

     // Split the array into two;
     for (int i = 0; i < firstPart; i++)
     {
                                                                                                                                                                                                                                                                                                                                                                                                                  strings1[i] = mer[i];
     }

     for (int i = firstPart; i < mer.Length; i++)
     {
         strings2[i - firstPart] = mer[i];
     }

     strings1 = Mergesort(strings1);
     strings2 = Mergesort(strings2);

     int j = 0;
     int k = 0;

     for (int i = 0; i < sorted.Length; i++)
     {
         if (j == strings1.Length)
         {
             sorted[i] = strings2[k];
             k++;
         }
         else if (k == strings2.Length)
         {
             sorted[i] = strings1[j];
             j++;
         }
         else if (stringcompare(strings1[j], strings2[k]))
         {
             sorted[i] = strings1[j];
             j++;
         }
         else
         {
             sorted[i] = strings2[k];
             k++;
         }
     }

     return sorted;
 }
        
}*/</string></string>