public partial class MainWindow : Window
{
     // memebers
     public FtpWebRequest _ftpRequest;
     public FtpWebResponse _ftpResponse;
     public Stream _responseStream;
     public int _pos = 5;
     public int _need_read_byte = 6;

     public MainWindow()
     {
          InitializeComponent();

          // status
          this.Status.Content = "FTP not connected";
          this.Url.Text = "ftp://";
     }

     private void Connect_Click(object sender, RoutedEventArgs e)
     {
          String strURL = this.Url.Text;
          String strLogin = this.Login.Text;
          String strPassword = this.Password.Text;

          try
          {
               // create ftp connection
               _ftpRequest = (FtpWebRequest)WebRequest.Create(strURL);
               _ftpRequest.Credentials = new NetworkCredential(strLogin, strPassword);

               // ftp method
               _ftpRequest.Method = WebRequestMethods.Ftp.DownloadFile;

               _ftpRequest.ContentOffset = _pos; // offset

               // get ftp response
               _ftpResponse = (FtpWebResponse)_ftpRequest.GetResponse();

               // get stream
               _responseStream = _ftpResponse.GetResponseStream();

               // show result
               this.Status.Content = "FTP succecfull";
          }
          catch (Exception exc)
          {
               MessageBox.Show(exc.Message);
          }

     }

     private void GetData_Click(object sender, RoutedEventArgs e)
     {
          try
          {
               // read file
               byte[] buffer = new byte[1024];
               int result_read_byte = _responseStream.Read(buffer, 0, _need_read_byte);

               // split
               buffer = buffer.Take(result_read_byte).ToArray();

               // convert to string
               string fileString = System.Text.Encoding.UTF8.GetString(buffer);

               // show result
               this.Status.Content = "Прочитано " + result_read_byte + " байт " + " с позиции " + _pos;

               this.DataText.Text = fileString;

               // pos
               _pos += result_read_byte;
          }
          catch(Exception exc)
          {
               MessageBox.Show(exc.Message);
          }
     }
}