DWF is an "digital plot" file. And like you can digitize/vectorize/scan a paper drawing, you can also convert/recover DWF files back to DWG (using third party utilities) - but in both cases you will loose substantial amount of information, structure and precision of the original drawing.
Both DWF/DWFx and PDF were meant to be used as reference (read-only, unchangeable) drawings - you can underlay them directly in AutoCAD (like xrefs), switch their layers, etc.
Conversion to the editable DWG format is not an intended operation with DWF files. DWF is a vector format containing only "low-intelligence" (plotting) entities so it cannot be fully recovered (changed) back to a standard DWG drawing.
Nevertheless, you can try the ICDWFIN [url verified 2/2005] or the DWF Importer [url verified 2/2005] or the DWF to DWG Converter [url verified 6/2005] to read your DWFs back into AutoCAD.
DWF files with markups from DWF Composer (Design Review) can be read/displayed (round-trip) in AutoCAD/ADT/Map (2005+) and Revit (8+). Run the Markup manager (Ctrl+7) and switch to the DWF geometry (Alt+4).
Since AutoCAD 2007 you can directly read in (attach, import) a DWF file into AutoCAD using the DWFATTACH command.
Since AutoCAD 2009 you can use _DWFATTACH to attach (underlay) also DWFx files. The DWF/DWFX/PDF underlay functionality is now integrated in the AutoCAD XREF manager.