public const int WM_KEYDOWN = 256;
public const int WM_KEYUP = 257;
private void button1_Click(object sender, EventArgs e)
{
webBrowser1.Focus();
keybd_event(Keys.ControlKey, 0, 0, 0);
keybd_event(Keys.A, 0, 0, 0);
PostMessage(webBrowser1.Handle, WM_KEYDOWN, Keys.A, 0);
keybd_event(Keys.ControlKey, 0, KEYEVENTF_KEYUP, 0);
}