how to get handle to a window

for reflecting the changes after re-sizing the window, how to get handle to the window in C# 

// this is the code for opening a file and display in hexadecimal format
       public void open()
       {
           string chosen_file = "";
           ofd.Title = "Open a file";
           ofd.FileName = "";
           ofd.Filter = "Text Files(*.txt)|*.txt|Rich Text Box(*.rtb)|*.rtb|Word Document(*.doc)|*.doc|HTML Pages(*.htm)|*.html|Cascading Style Sheet(*.css)|*.css|JAVA(*.java)|*.java|video file(*.wmv)|*.wmv|All Files(*.*)|*.*";
           if (ofd.ShowDialog() == DialogResult.OK)
           {
               chosen_file = ofd.FileName;
               // richTextBox2.LoadFile(chosen_file, RichTextBoxStreamType.PlainText);

               var fileInfo = new FileInfo(ofd.FileName);
               fileInfo.Length.ToString();
               //  MessageBox.Show(new FileInfo(ofd.FileName).Length.ToString());
               byte[] buffer = new byte[fileInfo.Length];

               {
                   int length = (int)fileInfo.Length;
                   FileStream fileStream = new FileStream(ofd.FileName, FileMode.Open, FileAccess.Read);
                   fileStream.Read(buffer, 0, length);
                   string bb = "";
                   int i = 0;
                   //int numBytesToRead = buffer.Length; ;
                   while (i < buffer.Length)
                   {
                       if ((i % 16) == 0)
                       {
                           bb = bb + "\n";
                           bb = bb + i.ToString("X8");
                           bb = bb + "\t";
                       }
                       else if ((i % 4) == 0)
                       {
                           bb = bb + "\t";
                       }
                       bb = bb + buffer[i].ToString("X2"); // modified on 30june2014
                       // if ((i % 4) == 0)
                       // {
                       //
                       // }
                       i = i + 1;
                   }
                   richTextBox2.Text = bb;
               }

// this is the code for resizing but it has some problems 
//1. how to fetch the data and how to convert the data 

        private void PaintForm_Resize(object sender, System.EventArgs e)
        {
            //Width = 580;
            //Height = 487;
            //string []buffer =new byte[ richTextBox2.Text];
            //byte[] buffer2 = Encoding.Default.GetBytes(richTextBox2.Text);
         
            
            //int scaleX = this.Width / 100;
            //int scaleY = this.Height / 100;
            //paintImage.SetBounds(5 * scaleX, 5 * scaleY, 70 * scaleX, 75 * scaleY);
            //controlPanel.SetBounds(80 * scaleX, 5 * scaleY, 15 * scaleX, 75 * scaleY); 

           
            byte[] buffer = new byte[richTextBox2.Text.Length];
                      
            //  int length = (int)richTextBox2.TextLength;
            //  int length = (int)buffer.Length;


            //filestream filestream = new filestream(ofd.filename, filemode.open, fileaccess.read);
            //filestream.read(buffer, 0, length);

            //From byte array to string

            string bb ="";
            int i = 0;
            //int numBytesToRead = buffer.Length; 
            while (i < buffer.Length)
            {
                if ((i % 8) == 0)
                {
                    bb = bb + "\n";
                    bb = bb + i.ToString("X8");
                    bb = bb + "\t";
                }
                else if ((i % 4) == 0)
                {
                    bb = bb + "\t";
                }
                bb = bb + buffer[i].ToString("X2");
                // bb = bb + richTextBox2.Text[i].ToString("X2");

                i = i + 1;
            }

            richTextBox2.Text = bb;

          
        }