This functionality can be blocked through ACL and OIR as per PTC standards. However, looking at your snapshot seems that it most probably is related to OIR as the Access rule for removing the modify access for the number is bundled with the filename too. Please check if the OIR pertaining to that context for EPMDocument. the number field might have a Immutable Contraint added which will override the access given to hide the option in the UI. This functionality works till10.2 but isn't working in WC11.