You first have to figure out what data format .sf is.
I'm unfortunately not aware of these .sf extension.
Cadence Virtuoso currently support two layout exchange
formats.
First, most common used in industry GDSII 'Graphic Data System' (File -> Import/Export -> Stream),
for further information have a look at Cadence Online Docu (cdsdoc)
Design Translators Reference, Appendix A Stream Format
Second CIF 'Caltech Intermediate Form' (File -> Import/Export -> CIF),
http://caltechcstr.library.caltech.edu/431/which is more used for education on Universities because it is an ASCII format and you can hack it whether GDSII is binary.
Bernd