Extension For Standard PO Invoice Printmanagement Report in D365

Dear All I need to add 2 fields in standard purchase order invoice report with out disturbing standard one, so i duplicate the report and extended the DP class but how should i extend the controller class ???

Because for Print Management Report we need to write condition to print our Customized report name like below

if(_jourTable.TableId == tableNum(VendInvoiceJour))
{
printSettingDetail.parmReportFormatName("VendInvoiceDocument.ReportNew");
}

Please Suggest me how to extend Form letter report Class or else how to achieve this 

Thanks in Advance..