I asked that question: https://superuser.com/questions/1842310/collaborate-on-a-ms-word-document-while-prohibiting-word-online

It has been closed. But it seems, by reading all the comments, that the answer is "It is impossible". I think if anyone is wondering the same question, they'd be glad to have this answer.

Do you think we should re-open this question to answer that is impossible or let it closed?