2 Answers

Design Web Format (DWF) is a secure file format developed by Autodesk for the efficient distribution and communication of rich design data to anyone who needs to view, review, or print design files. Because DWF files are highly compressed, they are smaller and faster to transmit than design files, without the overhead associated with complex CAD drawings (or the management of external links and dependencies). With DWF functionality, publishers of design data can limit the specific design data and plot styles to only what they want recipients to see and can publish multisheet drawing sets from multiple AutoCAD drawings in a single DWF file. They can also publish 3D models from most Autodesk design applications.
DWF files are not a replacement for native CAD formats such as AutoCAD drawings (DWG). The sole purpose of DWF is to allow designers, engineers, project managers, and their colleagues to communicate design information and design content to anyone needing to view, review, or print design information – without these team members needing to know AutoCAD or other design software.
The current AutoCAD file format (.dwfx) is based on ISO/IEC 29500-2:2008 Open Packaging Conventions.

Read more :http://en.wikipedia.org/wiki/Design_Web_Format

For opening/reading .dwg files you may use dwg restore

Tool http://www.dwg.recoverytoolbox.com will be useful for you