Ramesh,
Yes by using Trigger you have to subscribe the broker publishable document.So create a trigger with publishable documenttype and specify subscribing service name.This will trigger when ever particular broker document got published (pub/sub model).
Please note subscribe flow service input should be fully qualified publishable documentName(folder.subfolder: publishdocNameDocumentReference) so that you can map source publishable document to target format what ever it is.
For debugging purpose put a savepipeline in the subscribe service to make sure trigger is working as expected and you should see that document in the pipeline.
HTH,
RMG
#webMethods#Integration-Server-and-ESB#Universal-Messaging-Broker#broker