Running a method in BackGroundWorker and Showing ProgressBar

Instead of using one ParseFiles method (which should depend on myBGWorker) use loop and method which parse one file. Report progress percentage in that loop:

private void parseButton_Click(object sender, EventArgs e)
{
    parseButton.Enabled = false;
    myBGWorker.RunWorkerAsync();
}

private void myBGWorker_DoWork(object sender, DoWorkEventArgs e)
{
   for(int i = 0; i < filesCount; i++)
   {  
       ParseSingleFile(); // pass filename here
       int percentage = (i + 1) * 100 / filesCount;
       myBGWorker.ReportProgress(percentage);
   }
}

void myBGWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    myProgressBar.Value = e.ProgressPercentage;
}

void myBGWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    parseButton.Enabled = true;
    MessageBox.Show("Done");
}