"The user logged into CorVu when the CorPortfolio file was created becomes the owner who has the full set of permissions. The owner can assign any CorVu user or user group a mix of permissions. If you do not set up such permissions, other CorPortfolio users are assigned read-only access."
So basically you need to login to CorVu using the SAME userid that was used by the original creator of the CorPortfolio document if you want full access to edit it.
The screengrab below shows the CorPortfolio Permissions panel for a file called CareerMap.cbr (each file can have different settings).
To give another CorVu account full access, use menu File>Security to open the panel, then click on the Write option, then drag & drop a user or group to the Access box - see pic.