Sheets and Hypermodeling
The hypermodeling feature gives you the ability to insert PDF sheets(2D plans) in the online Viewer. Using this feature you will be able to visualize 3D and 2D elements at the same time. Sheets(2D Plans) can be inserted using two methods: Automatically using the add-in or by uploading a PDF file in the Viewer and positioning it manually.
Here are a few article that will guide you with the setup of the hypermodeling in your project: