The Compound Document Framework uses a data replication model for its synchronous collaboration. Each user has their own copy of the data with all changes being propagated to all collaborators.
You do not need to do anything special when opening a document other than to specify sharing mode. A local copy is created for each collaborator (except the first, who edits the original) when the document process is started. The temporary copy is deleted by the CommonPoint application system when you end your part of the collaboration.