void btnPrint_Click(object sender, RoutedEventArgs e)
{
       PrintDocument pd = new PrintDocument();
       pd.PrintPage += new EventHandler<PrintPageEventArgs>(pd_PrintPage);
       pages.Add(grdMain);
       pd.Print("Title1");
}

void pd_PrintPage(object sender, PrintPageEventArgs e)
{
      e.PageVisual = grdMain;
      e.HasMorePages = true;
}