Use FileStream to read a file byte by byte : FileStream « File Directory Stream « C# / CSharp Tutorial

1. C# / CSharp Tutorial
2. File Directory Stream
3. FileStream

using System;
using System.Windows.Forms;
using System.IO;

class MainClass
{
  public static void Main() 
  {
    OpenFileDialog dlgOpen = new OpenFileDialog();
    dlgOpen.Title="Select file to back up";

    if (dlgOpen.ShowDialog() == DialogResult.OK)
    {
      FileStream inStream = File.OpenRead(dlgOpen.FileName);
      FileStream outStream =  File.OpenWrite(dlgOpen.FileName + ".bak");
      int b;

      while ((b = inStream.ReadByte()) > -1)
        outStream.WriteByte( (byte) b);

      outStream.Flush();
      outStream.Close();
      inStream.Close();
    }
  }
}