I need help dwf file to convert step ,dwg,igs ,etc.......

It depends of wich version you are using.
In AutoCAD 2012 & 2013 you can export drectly by hitting file>export>choose filetype et voila....

Regards

to export, you need to open the file first.
How it is possible to open dwf in autocad? as far as i know, this is not 3D data file, its an edrawing that could be opened by publisher, design rewiever, etc.

If somebody knows any valuable solution, please do not hesitate to share with it.

I found one, maybe it'll help somehow. But it still seems to me only a way around.
I opened the 3D DWF file in navisworks viewer, and then exported to FBX, the format which opens well in 3ds max, in turn max has no problem in saving to e.g. DWG, OBJ, STL, SAT.
DWG opens fine in Autocad, exports to step fine.
For my example it took a lot of time unfortunetly and increased the DWG size compared to original, but it's worth the effort in some cases,
BR, Chris

PS I checked that autocad opens FBX files as well