Unable to show PDF files in Generate Extensible Work Order Traveler Report

We have customized Generate Extensible Work Order Traveler Report. We have a requirement to print PDF documents attached with in the work order operations / work instructions. As we can see if generate using Print Work Order Traveler report it shows the PDF file. But Print Work Order Traveler we are not able to see any data model, so unable to get the logic for it. We need to implement the similar logic to Generate Extensible Work Order Traveler Report.