There is only one file type that uses the .OBD extension:
Office Binder Document
File created by Office Binder, a program used to link common Microsoft document file types together; stores a "binder," which includes a collection of Office document objects; used for linking document content together from Microsoft Word, Excel, PowerPoint, Project, and Visio files.
NOTE: Office Binder is included with Microsoft Office 95, 97, and 2000, but it is no longer supported in newer versions of Microsoft Office. Microsoft provided a downloadable tool called Unbind, which can still open OBD files in Office 2003.
Updated: July 2, 2011