PDF file transfer using web service

Hi,

We are using ABAP web service (through function module) to transfer some data from ECC to a portal system which is Non-SAP system.

One of the requirement is to send Invoice print out in PDF format through web service?

Can we achieve that?

I know we can create a spool and convert that spool to PDF binary format using FM  CONVERT_OTFSPOOLJOB_2_PDF.

But once data is converted, I checked within SAP in debug mode, it is coming in some non-readable format.

WSDL file is not able to interpret that data for front end system and front end system is giving error "http/1.1 500 internal server error"

Any pointer on this will be highly appreciated.

Thanks

Puneet