Working Holiday Visa is designed for nationals of certain countries (based on bilateral agreements between Hong Kong and those countries) . A Working holiday visa allows you to stay in Hong Kong for up to 12 months, during which period you can take up employment with up to 4 employers (not more than three months per employer).
The goal of a working holiday visa is cultural exchange. So the Immigration Department does not anticipate for you to get involved in freelance work or entrepreneurship. Consequently,applying to incorporate a company and engaging in business is not a permitted activity.
If you plan to stay in Hong Kong long-term and engage in business activity, you should consider applying for a business investment visa. Up to that moment, it is strongly suggested you do not get involved in any business activity in Hong Kong, as it may affect the success of your application.