Which software does mold designers use to design mold?

You can use Solid works, Catia, Uni Graphics & Pro Engineer for mold design

You can use also Autodesk Inventor

There are a lot of softwares for me its best to use ProE or CATIA

YOU CAN USE NX siemens " Mold Wizard " also Autodesk inventor mould and this programs depens on steps so it i easy and powerfull or you can use Power Shape and Power Mill for mould cad and cam