Does someone receiving an Office document with an embedded DWF need a DWF viewer?

Yes. It is necessary for the person to have the Autodesk DWF Viewer or Autodesk Design Review. The DWF file is embedded in the Office document, so you don't have to send the DWF file separately; however, the recipient of your Office document will need to install a viewer on his system. The Microsoft Office application will invoke the Autodesk DWF Viewer ActiveX Control inside of the office application. This allows the DWF file to be viewed within the context of the Office file such as a Word document, Excel workbook, or PowerPoint presentation.