private void button1_Click(object sender, EventArgs e) { object format = 5;//Nothing value. ApplicationClass xlApp = new ApplicationClass(); Workbook xlBook = xlApp.Workbooks.Open("D:\\WORKS\\App\\bin\\Debug", 0, false, format, null, null, false, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, null, true, false, 0, true, false, false); Sheets xlSheets = xlBook.Worksheets; Worksheet xlSheet = (Worksheet)xlSheets.get_Item("Sheet1"); // open Sheet1. xlApp.Visible = true; }