To take advantage of the entire feature set in ForNAV, and design report objects with the ForNAV Designer, you must have access in the Dynamics NAV license to export and import text objects.
If you use the Open Designer option on the request page, you must have export/import permissions in the NAV license that is uploaded to the server.
With C/SIDE, you can design the report object and select the view layout from the menu. This only requires that you have export/import permissions in the NAV license that you point to from C/SIDE.
These two options mentioned above are mostly for NAV developers (that is, NAV partners with a NAV developer license, or customers who have added either the Application Builder or the Solution Developer granule to their NAV license).
End customers with a standard Dynamics NAV license (that is, without the Application Builder or the Solution Developer granule in the NAV license), can edit and design existing ForNAV reports using the Custom Report Layouts feature. You can read more about that here: Working with ForNAV reports in the custom report layouts window