Documents in GlobalAction workflows can be viewed just like any other document, assuming appropriate permissions for a given user. Workflows do introduce an additional level of security through the use of Queues. When a document is current being processed by the GlobalAction Engine, or is in a Queue the user does not have permissions on, the Viewer will display a status message at the bottom of the Index panel.
This status message should serve as a warning to the user that their ability to interact with the document at this time might be impacted by the Document's current state in the workflow. By hovering the mouse cursor over the status, a more detailed message will pop up.