public class PrintDocumentGridRenderer 

// print two grids into an existing PrintDocument
private void button1_Click(object sender, EventArgs e)
{
  using (var dlg = new PrintPreviewDialog())
  {
    dlg.Document = this.printDocument1;
    dlg.ShowDialog(this);
  }
}
            
// event handlers for the PrintDocument object on the form
PrintDocumentGridRenderer _g1, _g2;
void printDocument1_BeginPrint(object sender, System.Drawing.Printing.PrintEventArgs e)
{
  // create and configure grid renderer for the first grid
  _g1 = new PrintDocumentGridRenderer(c1FlexGrid1);
  _g1.Options = PrintGridFlags.FitToPageWidth | PrintGridFlags.ExtendLastCol;
  
  // create and configure grid renderer for the second grid
  _g2 = new PrintDocumentGridRenderer(c1FlexGrid2);
  _g2.Options = PrintGridFlags.FitToPageWidth | PrintGridFlags.ExtendLastCol;
}
void printDocument1_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
{
  // render first grid
  if (_g1.CurrentPage < _g1.PageCount)
  {
    _g1.PrintPage(e);
    e.HasMorePages = true;
  }
  
  // render second grid
  else if (_g2.CurrentPage < _g2.PageCount)
  {
    _g2.PrintPage(e);
    e.HasMorePages = _g2.CurrentPage < _g2.PageCount;
  }
}