DWF and DWFx are secure file formats developed by Autodesk to combine and publish rich 2D- and 3D-design data for sharing with others.
DWF and DWFx are highly compressed file formats and hence more suitable than DWG files for distributing over the Internet for review. You can export a single drawing or publish multiple drawings and sheet sets into a single DWF or DWFx file.
Reviewers don't need to install AutoCAD to review DWF and DWFx files. Instead, they can install the free program, Autodesk Design Review, to view, mark up, print, and track changes. You can read the markups in AutoCAD, change your drawings, change markup status, and republish to DWF or DWFx for further review cycles.
DWFx is the newest version of the DWF file format. DWFx is based on the XML Paper Specification (XPS), and hence can be viewed and printed with the Microsoft XPS Viewer. The XPS Viewer is a free program that is distributed with the Windows Operating System.
DWFx files are typically larger than the corresponding DWF file. You typically use the DWFx file format to share design data with reviewers who cannot install Autodesk Design Review.