No, workpapers are not restricted to just those assigned to them.
Firm-wide Access: By default, anyone in the firm can view all workpapers, including their worksheets, comments, history, and other details.
Private Workpapers: If a workpaper is marked as private, only those assigned to it can access its contents. However, private workpapers will still appear in the firm’s Workpapers List, but other users will not be able to open or view their details.