With the proper permissions, a user can check "public" on the document creation/editing form, to designate it as public.
Since that functionality introduces new possibilities of abuse, of copyright, etc, we have constrained the availability of that feature to administrators. For now in other words, we can do this for you, and as we build out more moderation features/capacities, we anticipate opening up the feature more broadly.
If you have a document you'd like to have me make public, send me the URL, and I will get it done for you!
(Sorry for the slow response, by the way. I was away on vacation, and am now back!)