MUC specification doesn't have support for file transfer/sharing.
Thanks for your answer.
I have 2 more questions:
1. how can I enable/implement this? (sharing files in MUC)? is there a plugin can do this?
2. what is the reason behind of it why it is no supported? specification doesn't have it, but other servers can do, why not in openfire? does openfire have the plan to do it?
1. I'm not a developer, so can't help with that. Not aware of a plugin to do this.
2. I don't know. Maybe it is planned for some new MUC specification version. But i don't see anything about file transfer/sharing in this XEP-0045: Multi-User Chat Do you mean some other xmpp server supports this? One of these? https://xmpp.org/software/servers.html Or do you mean something else, not a xmpp server? I'm not aware of a plan to do it (and first of all it has to make its way to specifications i think, to be planned at all).