Abad was on the Dean's honor list at the
Ateneo de Manila University, where he earned his law degree in 1968. He is a member of the Fraternal Order of Utopia. He first engaged in private practice at the Jose W. Diokno Law Office in 1968, and then he joined the government, working as Technical Assistant (1969–1973) and Associate Attorney (1974–1975) at the Supreme Court, supervised by then Chief Justice
Fred Ruiz Castro. In 1975, he joined the
Office of the Solicitor General (OSG). In 1985, he was promoted to Assistant Solicitor General, a post he held for about a year before setting up his own law firm. He has rendered free legal aid for the
Free Legal Assistance Group (FLAG), Department of Social Welfare and Development, and the Angels of Hope Orphanage, Pulong Bunga, Silang, Cavite. He has conducted weekend training for lay and religious catechists for the
Archdiocese of Manila. From 1988 to 1990, he worked as legal consultant for the presidential committee on the nuclear power plant under the late Justice Secretary Sedfrey Ordoñez. Later, he worked as counsel for the Equitable Banking Corporation and its officers and branch managers during the impeachment trial of former President Joseph E. Estrada. Prior to his retirement, he penned the High Court's ruling in
Disini v. Secretary of Justice on the contentious
Cybercrime Prevention Act of 2012, a landmark decision. ==Teaching career==