You must learn different softwares related to Compiter Aided Design (CAD) to get job in Mechanical CAD. There is good oppurtunity for CAD Engineer if he/she knows different modelling softwares. CAD is mainly related to modeeling, assembly and drafting of various 3D objects. You can get job in automotive industries, as CAD softwares are used by automotive industries most. Other industries are like aerospace industries, Casting die making industries etc.