With a unique background in computer science and law, Dr Pun is an expert on legal issues arising from information technology and electronic commerce. He is the pioneer of the course "Legal Aspects of Computing" in the Computer Science Department, the first of its kind in Asia when it was launched in 1993. He is a seven-time recipient of the Department's Teaching Excellence Award. In 2002, he became the first teacher in the Engineering Faculty to receive the honour of University Teaching Fellow for his teaching excellence and contributions to university education. From 2002 to 2014, he was a founding co-director of the Law & Technology Centre jointly established by the Department and the Law Faculty. He had also taught in the Law Department during 2000-2011, lecturing in intellectual property law and information technology law.
Dr Pun is the author of Software and Copyright (Joint Publishing Hong Kong, 1996, in Chinese), the first book on the subject of copyright protection for computer software in Hong Kong, and Annotated Patents Ordinance (Butterworths, 2005). His other academic works have appeared in journals including European Intellectual Property Review, Computer and Telecommunications Law Review, Intellectual Property Quarterly, International Review of Industrial Property and Copyright Law and Hong Kong Law Journal. He has been interviewed and invited to speak on many occasions regarding intellectual property and information technology issues.
Dr Pun was called to the Hong Kong Bar in 1999. He had appeared as counsel in cases involving copyright, registered design, trademark, passing-off, patent, trade libel, contract, conveyancing, adverse possession, company matters and employment disputes. He was the defence counsel before the Court of Final Appeal in Chan Nai Ming v HKSAR  3 HKC 255, the first criminal case in the world concerning the use of BitTorrent on the Internet. From 2007 to 2013, he was appointed by the Chief Executive as a member of the Unsolicited Electronic Messages (Enforcement Notices) Appeal Board, a statutory body constituted under the Unsolicited Electronic Messages Ordinance (Cap. 593).
Dr Pun retired from his full time position at the Computer Science Department in July 2016. He is currently an Honorary Associate Professor in the Department teaching at both the undergraduate and postgraduate levels, as well as a private legal consultant providing advice to law firms, corporate bodies and individual clients.