foreach (string fileName in System.IO.Directory.GetFiles(path))
{
    System.IO.FileInfo fileInfo = new System.IO.FileInfo(fileName);

    fileInfo.Attributes |= System.IO.FileAttributes.ReadOnly;
    // or
    fileInfo.IsReadOnly = true;
}

foreach (string fileName in System.IO.Directory.GetFiles(configFilePath))
      {
          System.IO.FileInfo fileInfo = new System.IO.FileInfo(fileName);
          if(fileInfo.IsReadOnly==true)
          fileInfo.IsReadOnly = false;
      }