Using protobuf in workflow/activity

Is there an example of using protobuf generated message in workflow /activity ? Does it have out-of-the-box converter so that the payload can be sent / received ?

I am afraid there is not a specific example, but yes Java and Go both support Protobuf-spec’d JSON serialization out of the box. In fact, single Proto-based messages for request and response to both workflows and activities is very much encouraged for contract change compatibility and cross-language compatibility.