[support] Document Management in drupal

am working on a corporate intranet and drupal has proved to be very useful so far, i have been looking at the diffeent modules available but i cant seem to find one that will handle documents easily ( upload, view and share word, PDF Excel etc, on different user roles, just like KnowledgeTree<http://www.knowledgetree.com>) My question is, does such a module exist? and if not, is there a way to intergrate KnowledgeTree into drupal such that a user has to sign in only once? -- David Njuki.