Issue:
1. You cannot delete viewports in Paper Space
2. If you try to Erase => All, if will leave the viewports, but will erase all data in Modelspace
This is currently a known defect in Civil 3D and is currently under review with the developers under these defect numbers:
CIVILX-178 - Erase All Defect
CIVILX-90 - Viewports are not erasable
If you encounter this issue, the only way to remove the viewports from Paperspace is to use the Cut (Ctrl +X) to remove them
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