Hi Priya,
1. It is possible to open popup from POWL, you can use method IF_FPM=>OPEN_DIALOG_BOX( )
Opening and Closing FPM Dialog Boxes - Floorplan Manager for Web Dynpro ABAP - SAP Library
2. If you want to download the file upon click on a link, you may use:
cl_wd_runtime_services=>attach_file_to_response( i_filename = <file_name> i_content = <file_content> i_mime_type = <mime_type> i_in_new_window = abap_true ).
Hope it helps. Cheers!