SOAP PI SOAP with Attachments

Hello Experts

I have a scenario, where I send a DocumentName in a request to PI. PI makes a webservice call, retrieves the document (.pdf) and sends it back to requester. I just wanted to confirm, if I should be using Java Mapping anywhere to read the .pdf file before sending it to requester?

Also, would using a HTTP GET or a REST adapter be a good idea?

Any pointers would be greatly appreciated.

Thanks

Jaya