A dxf is equivalent to a drawing. A dwf is an electronic print with layers. It cannot be converted back to a drawing. It can be underlaid and cropped into another drawing using AutoCAD.
Google and you will find some converters out there, some will let you test it a bit which would be the way to go. Another way, open the DWF and save out a PDF, then in AutoCAD you can IMPORT the PDF, which via the Settings dialog of the PDF Import you can have it come in as vectors.
