Microsoft.Office.Interop.Excel.Application ObjExcel = new Microsoft.Office.Interop.Excel.Application();
//Открываем книгу.
Microsoft.Office.Interop.Excel.Workbook ObjWorkBook = ObjExcel.Workbooks.Open(Filename: @"...", 0, false, 5, "", "", false, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "", true, false, 0, true, false, false);
//Выбираем таблицу(лист).
Microsoft.Office.Interop.Excel.Worksheet ObjWorkSheet;
ObjWorkSheet = (Microsoft.Office.Interop.Excel.Worksheet)ObjWorkBook.Sheets[1];