C#

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
        private struct Header
        {
            public byte version;
            public Int32 numRecords;
            public Int16 headerLen;
            public Int16 recordLen;
            public byte encryptionFlag;
            public Int64 reserved;
            ....
        }

using (OpenFileDialog of=new OpenFileDialog())
           {
               of.ShowDialog();
               FileStream fs = new FileStream(of.FileName,FileMode.Open,FileAccess.ReadWrite);
               BinaryWriter bw = new BinaryWriter(fs);
               BinaryReader br = new BinaryReader(fs);

               byte[] buffer = new byte[Marshal.SizeOf(typeof(Header))];

               buffer = br.ReadBytes(Marshal.SizeOf(typeof(Header)));
               GCHandle handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
               Header rHeader = ((Header)(Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(Header))));
               handle.Free();

               Header wHeader = rHeader;
               wHeader.numRecords = 5;
               IntPtr ptr = Marshal.AllocHGlobal(buffer.Length);
               Marshal.StructureToPtr(wHeader, ptr, true);
               Marshal.Copy(ptr, buffer, 0, buffer.Length);
               Marshal.FreeHGlobal(ptr);

               bw.Seek(0, SeekOrigin.Begin);

               bw.Write(buffer);
               bw.Close();
               br.Close();
               fs.Close();
           }

protected override void OnPaintBackground(PaintEventArgs e)
    {

    }
    private Bitmap _cachedBitmap;
    protected override void OnPaint(PaintEventArgs e)
    {
        using (Graphics g = e.Graphics)
        {
            if (!_isPainted)
            {
                _cachedBitmap = new Bitmap(ClientRectangle.Width, ClientRectangle.Height);
                InitilizeBitmap(g);
                _isPainted = true;
            }

            //Rectangle to show a particular portion of bitmap.
            Rectangle rec = new Rectangle(0, _bitmapLocation.Y, ClientRectangle.Width, ClientRectangle.Height);
            //using (Graphics gCached = Graphics.FromImage(_cachedBitmap))
            //{
            //   gCached.Clear(BackColor);
            //   gCached.DrawImage(_bmpControl, 0, 0, rec, GraphicsUnit.Pixel);
            //}

            //g.DrawImage(_cachedBitmap, 0, 0);
            g.DrawImage(_bmpControl, 0, 0, rec, GraphicsUnit.Pixel);
        }
    }