SAP GW - Download file by using execute action

Hello Experts,

I've the following scenario:

I need to send some header and table data (as input to GW service) and get a file (in my case it's PDF file but it could be any other file).

I'm aware of file download option (by using get_stream) in GW but in the case I need to use execute_action.

How can I define an entity/complex entity or any other data structure that will return a file (I tried to define an entity with xstring field and set relevant header fields (content type etc) but it seems that the gateway framework classes that runs AFTER my custom DPC class code is changing it).

Regards,

Omri