In SharePoint you can't start a workflow on an item that is in a checked out
state, (at least not a Designer created workflow). The check-in, check-out
functions of the workflow allow you to make column edits to the metadata of an
item, which if the item exists in a library that requires check-out, must be
checked out prior to making any such changes. So, If you want to edit an item,
the workflow can first check it out, make its changes, and then check that item
back in. However, the item must be in a checked in state in order for the
workflow to even begin.
You can't do what it is you are trying to accomplish. A small clarification on
what Paul stated. Items are only stored in your local drafts folder if you have
set Word to do this. This is the default behavior, but you can modify Word to
not use the local drafts and instead keep the document on the server.