fpSpread1.SaveExcel("Excel.xlsx", FarPoint.Excel.ExcelSaveFlags.UseOOXMLFormat | FarPoint.Excel.ExcelSaveFlags.SaveAsFiltered);

private void button1_Click(object sender, EventArgs e)
{
    FarPoint.Win.Spread.FpSpread tempSpread = new FarPoint.Win.Spread.FpSpread(FarPoint.Win.Spread.LegacyBehaviors.None);
    tempSpread.Sheets.Count = 1;

    fpSpread1.Sheets[0].ClearSelection();
    fpSpread1.Sheets[0].AddSelection(0, 0, fpSpread1.Sheets[0].RowCount, fpSpread1.Sheets[0].ColumnCount);
    fpSpread1.Sheets[0].ClipboardCopy(FarPoint.Win.Spread.ClipboardCopyOptions.AsStringSkipHidden);
    tempSpread.Sheets[0].ClipboardPaste();
    tempSpread.Sheets[0].ClearSelection();
    fpSpread1.Sheets[0].ClearSelection();

    tempSpread.SaveExcel("Filtered.xlsx", FarPoint.Excel.ExcelSaveFlags.UseOOXMLFormat | FarPoint.Excel.ExcelSaveFlags.SaveAsViewed);
}