You can open several data files in one program tab. To do this, find on the right program panel the 'Multi window' section and select the multiview mode:
The 'Three views' mode selected on the screenshot above.
You can drag previously opened data from 'Services' section and drop it into any of empty views.
Selected view has the white bounding frame around it.
If you want to to select and take control over the view with opened data, click on that view.