Mounting an MDF disc image file outputs: "convert to *.iso format", so I use mdf2iso which gives:
$ mdf2iso obraz.mdf
mdf2iso v0.3.1 by Salvatore Santagati
Licensed under GPL v2 or later
Unknown format for obraz.mdf
I haven't found any solution to that problem, although other users had this same bug. Any piece of advice?