The Publish-Subscribe pattern/model is same as Application Event in Lighting Component. If you want to communicate between components those are not bounding in parent child relationship, but available in same page (say, in same app-builder page), then we will use publish-subscribe pattern. Here Salesforce already publish a pubsub.js file which we will use. 

The PowerForm is a way to create a self-service document for signature without writing any code. A PowerForm is initiated from a unique, secure URL that you make available for signers to complete.