When working with multiple models, the Active Document function allows you to select which SketchUp document is active within the Enscape User Interface (UI). This functionality helps you to switch within projects once the Enscape render window is open.
Active Document button in SketchUp
If you have multiple SketchUp documents open, you can then click the Active Document button and you will be able to see how many SketchUp documents are open at that moment. A check mark on one of these documents would indicate which document is currently active within the Enscape UI.
You can click and select any of the listed open SketchUp documents to switch and activate them in the Enscape UI. Once a new document is made active in Enscape, you would still have to go to the SketchUp project window manually. This feature helps achieve faster workflows when working within multiple projects simultaneously.