the RO environment is accessed via a specific read-only URL, for example: https://<docuware-server>.<my.domain>/DocuWare/PlatformRO/WebClient/ instead of https://<docuware-server>.<my.domain>/DocuWare/Platform/WebClient/
There is no specific license you need to assign to a user, just log in with the above URL.
Greetings from Germany,
Simon H. Hellmann
DocuWare System Consultant