private string GetModifyDateExcel(string fullPath) { // Require both wkbs and wkb // If these vars are not declared, Excel instances do not close properly Excel.Application xlApp; Excel.Workbooks xlWkbs = null; Excel.Workbook xlWkb = null; try { xlApp = new Excel.Application() { DisplayAlerts = false, Visible = false }; } catch { return(appInstanceFail); } try { xlWkbs = xlApp.Workbooks; xlWkb = xlWkbs.Open(fullPath, false, true); return(xlWkb.BuiltinDocumentProperties("Last Save Time").Value.ToString() != "" ? xlWkb.BuiltinDocumentProperties("Last Save Time").Value.ToString() : blank); } catch { return(cannotOpen); } finally { if (xlWkb != null) { xlWkb.Close(false); Marshal.ReleaseComObject(xlWkb); } if (xlWkbs != null) { Marshal.ReleaseComObject(xlWkbs); } if (xlApp != null) { xlApp.Quit(); Marshal.ReleaseComObject(xlApp); } } }