Code:
using Excel = Microsoft.Office.Interop.Excel;
...
Excel.Application xlApp = new Excel.Application();
Excel.Worksheet xlWorkBook = xlApp.Workbooks.Open(templateFileReport);    
Excel.Worksheet xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
pivotTables = (Microsoft.Office.Interop.Excel.PivotTables)xlWorkSheet.PivotTables(Type.Missing);
Excel.PivotTable table = pivotTables.Item(1);
...