Save FileStream into MemoryStream

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

class MainClass
{
  
  public static void SaveMemoryStream(MemoryStream ms, string FileName)
  {
    FileStream outStream = File.OpenWrite(FileName);
    ms.WriteTo(outStream);
    outStream.Flush();
    outStream.Close();
  }

  public static void Main() 
  {
    FileStream inStream = File.OpenRead("c:\\text.txt");
    MemoryStream storeStream = new MemoryStream();

    storeStream.SetLength(inStream.Length);
    inStream.Read(storeStream.GetBuffer(), 0, (int)inStream.Length);

    storeStream.Flush();
    inStream.Close();

    SaveMemoryStream(storeStream, "C:\\text.txt" + ".bak");
    storeStream.Close();
  }
}