C#

using System.ComponentModel;
using System.Windows.Forms;

namespace TestBGW
{
    public partial class Form1 : Form
    {
        private BackgroundWorker backgroundWorker;
        private string testString;

        public Form1()
        {
            InitializeComponent();
            backgroundWorker = new BackgroundWorker();
            backgroundWorker.WorkerReportsProgress = true;
            backgroundWorker.DoWork += new DoWorkEventHandler(backgroundWorker_DoWork);
            backgroundWorker.ProgressChanged += new ProgressChangedEventHandler(backgroundWorker_ProgressChanged);
            testString = "A";
            backgroundWorker.RunWorkerAsync(testString);
        }

        void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
        {
            string passedThrough = (string)e.Argument;
            passedThrough = "B";
            backgroundWorker.ReportProgress(0, passedThrough);
        }

        void backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            MessageBox.Show(string.Format("{0} - {1}", testString, e.UserState));
        }
    }
}

const string SOURCE = @"D:\myFile.bin";
const string TARGET = @"D:\myNewFile.bin";
const string TOSEARCH = "4D-00-C8";
const string REPLACEWITH = "4D-00-20";

byte[] byteArray = File.ReadAllBytes(SOURCE);
string byteString = BitConverter.ToString(byteArray);
if (byteString.Contains(TOSEARCH))
{
  string newByteString = byteString.Replace(TOSEARCH, REPLACEWITH);
  string[] newByteStringSplitted = newByteString.Split('-');
  byte[] newByteArray = new byte[newByteStringSplitted.Length];
  for (int i = 0; i < newByteArray.Length; i++ )
  {
    newByteArray[i] = byte.Parse(newByteStringSplitted[i], NumberStyles.HexNumber);
  }

  File.WriteAllBytes(TARGET, newByteArray);
}

moein.serpico wrote:

but that field returned no value