Why fil not downloads fully in C# form app

private void pictureBox2_Click(object sender, EventArgs e)
{
FolderBrowserDialog Save = new FolderBrowserDialog();//Declaring the folder browsing dialog
Save.RootFolder = Environment.SpecialFolder.Desktop;//setting to desktop
if (Save.ShowDialog() == DialogResult.OK)//An if statement to to show the path in textbox
{
string Text = textBox1.Text.ToString();//formatting to string
string[] arry = Text.Split('/');//splitting /
string dad = arry[arry.Length - 1];
ad = dad.Remove(dad.Length - 5);
label5.Text = dad;
path = String.Format("{0}//{1}",Save.SelectedPath,ad);
WebClient wb = new WebClient();




wb.DownloadProgressChanged += new DownloadProgressChangedEventHandler(wb_DownloadProgressChanged);
wb.DownloadFileCompleted += new AsyncCompletedEventHandler(wb_DownloadFileCompleted);
wb.DownloadFileAsync(new Uri(textBox1.Text), path);

timer1.Start();

}


}

void wb_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{

timer1.Stop();

DialogResult dr = MessageBox.Show("Yukl?m? bitmisdir! Icra olunsun?", "Bitdi!", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
if (dr == DialogResult.Yes)
{
progressBar1.Value = 0;
Process.Start(path);
}

}

void wb_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
progressBar1.Value = e.ProgressPercentage;
label7.Text = e.BytesReceived.ToString() + " bayt";
label6.Text = e.TotalBytesToReceive.ToString() + "bayt";
label8.Text = e.ProgressPercentage.ToString() + "%";
}