If your trying to directly invoke a remote IS service from your local IS, take a look at pub.remote:invoke
If the document is in your local pipeline at invoke time, the remote service can use it as it’s input (the remote service needs to have this document type defined as it’s input…)
Or, probably the best way is to just expose the remote service as a web service by simply:
Creating a new “Web Service Descriptor” WSDL for your provider IS service.
Import/Create the WSDL on the consumer IS, this will auto generate pretty much everything for you.