If you don't trust the OSP (Open Specification Promise), ask for a patent license at Microsoft, this is for the "Word Binary File Format (.doc) Structure Specification":
Patents. Microsoft has patents that may cover your implementations of the formats. Neither this notice nor Microsoft's delivery of the documentation grants any licenses under those or any other Microsoft patents. However, the formats may be covered by Microsoft's Open Specification Promise (available here: http://www.microsoft.com/interop/osp). If you would prefer a written license, or if the formats are not covered by the OSP, patent licenses are available by contacting moc.tfosorcim|glpi#moc.tfosorcim|glpi.