Kofax Power PDF for Mac is a document-based application. With it, you can open existing PDF documents and create new ones.
You can also drag a PDF's file icon and drop it on the Kofax Power PDF for Mac icon in the Dock to open it.
To re-open a recently opened document, choose File > Open Recent and select from the list.
For information on opening a document stored in iCloud see iCloud and Cloud Storage.