Autodesk, by design, has it so you cannot do this. DWF is their web format version of the file. The web version has that limitation put on it so that only the originator has access to the dwg (original) version. There may be some "programs" that could do this this, but they would be considered "hacks" of the protected version.
"Whether you think that you can, or that you can't, you are usually right "
.. Henry Ford
FH . . .
You can change a .dwf to a .dwg, at least we can in R2000i. I don't know if you lose any settings or details, though.
The software you need is by IntelCAD, and it's called Dwf In.