using System;
using System.Windows.Forms;
using System.IO;
class MainClass
{
public static void Main()
{
FileStream inStream = File.OpenRead("C:\\test.txt");
FileStream outStream = File.OpenWrite("C:\\test.txt" + ".bak");
byte[] buf = new byte[4096];
int bytesRead;
while ((bytesRead = inStream.Read(buf, 0, 4096)) > 0)
outStream.Write(buf, 0, bytesRead);
outStream.Flush();
outStream.Close();
inStream.Close();
}
}