There are two verbs that generally mean ‘to witness’ or “to make an appearance”, which are used when one wishes to be formal or simply sound smart. Other possibilities to get the same point across are to use “assistir (a)” or “estar presente“.
Presenciar – To witness, to be present during.
Ex. Ele presenciou o assalto ontem.
Ex. He witnessed the assault yesterday.
Comparecer (can be followed by a/em/com) – To be present, to attend, to make an appearance.
Used a lot for appearing in court.
Ex. Eu não vou comparecer na próxima reunião.
Ex. I am not going to attend the next meeting.