The new File and URL field in SBM 11.2+ use field privileges rather than attachment privileges. This means that if the field has the attribute to "Allow Multiple Files/URLs" then if you can Add a new file/URL then you can also delete any other file (unless you use append only). By default it is not possible to have a form on a transition where some users would be restricted to adding files (append only) and other users could also delete.
