Workflow in web site.

I want to develop a web site with hyperlinks to documents. But, the trick is in that I need a workflow integrated.
For example. Lets say we have>
User A -> Boss of user A

And user A wants to modify a WORD document. He makes the changes, but inorder for the changes to take effect, the approval of his boss is required. When Boss approves, the old document has to be erased and the approved document will take its place.
Any help_? Know any open source programs/freeware that do it?