Setting up a receiveport A with a receive location that picks up the .pdf, and then set up a send port B that subscribes to messages received through receiveport A (this is done via filter on the send port) should do the trick.
Using a passthru pipeline on both receive and send ports makes BizTalk ignore the contents of the message (everything in BizTalk is a message, so by the time the .pdf has passed through an adapter, it would be referred to as a message until it once again leaves BizTalk)