Need Help!!

i got a virus which is hard to deal with it, it infects the AUTOCAD files called LISP and comes in this format “CAD.LISP” , its almost everywhere on my network now i dont know yet how to stop it or how to disinfect thoese files and i cant jst DELETE them cause they’r important and needed, i tried many anti-viruses but not yet solved..anyone got any advice for that?…any suggested software?…