I am a Mechanical -turned- marine engineer, and I have lots of technical material, both in PDF and Word format on topics ranging from mechanical engineering, marine engineering, electrical engineering, mechatronics, naval architecture and shipbuilding, automation, etc. This technical material should be very useful to students of mechanical and marine engineerinng and can also serve as reference material for practising engineers. How can I earn from my technical material and my both practical and theoritical knowledge in this field?