Mam problem z programem Excel Interop.

Excel.exe nie zamyka się, nawet jeśli ponownie wydam instancje.

Oto mój kod:

using xl = Microsoft.Office.Interop.Excel;


xl.Application excel = new xl.Application();
excel.Visible = true;
excel.ScreenUpdating = false;
if (wordFile.Contains(".csv") || wordFile.Contains(".xls"))
{
   //typeExcel become a string of the document name
   string typeExcel = wordFile.ToString();
   xl.Workbook workbook = excel.Workbooks.Open(typeExcel,
                                                oMissing,  oMissing,  oMissing,  oMissing,
                                                oMissing,  oMissing,  oMissing,  oMissing,
                                                oMissing,  oMissing,  oMissing,  oMissing,
                                                oMissing,  oMissing);
   object outputFileName = null;
   if (wordFile.Contains(".xls"))
   {
     outputFileName = wordFile.Replace(".xls", ".pdf");
   }
   else if (wordFile.Contains(".csv"))
   {
     outputFileName = wordFile.Replace(".csv", ".pdf");
   }

   workbook.ExportAsFixedFormat(XlFixedFormatType.xlTypePDF, outputFileName, 
                                 XlFixedFormatQuality.xlQualityStandard, oMissing,
                                 oMissing, oMissing, oMissing, oMissing, oMissing);

   object saveChanges = xl.XlSaveAction.xlDoNotSaveChanges;
   ((xl._Workbook)workbook).Close(saveChanges, oMissing, oMissing);

   Marshal.ReleaseComObject(workbook);
   workbook = null;
}

Widziałem to zMarshal.RealeaseComObject powinna być praca, ale nic. Jak mogę to naprawić?

Dziękuję Ci.