Catholic records were kept in Latin, while civil registration records are kept in Dutch (or French, depending on the time). But Catholic families often recorded the Latin version of the name as the official version with the civil authorities as well. Latin names often ended in -us (for men) or -a (for women).
So a person who was called Petrus Josephus in the official records, may well have been called Piet in his every-day life. Here are some other names with their Dutch given names.
Men: Johannes (Jan), Josephus (Josef), Theodorus (Dirk, Theo), Gerhardus (Gerrit, Geert, Gert), Stephanus (Steven, Stefan), Hendrikus (Henk, Hendrik), Adrianus (Ad, Adriaan, Aart, Janus).
Women: Catharina (Katrien, Kato, Toos), Johanna (Janna), Maria (Mia, Marie, Mietje, Riet), Adriana (Sjaan, Jaantje), Gertrudis (Geertruida, Trui), Magdalena (Lena), Margaretha (Margriet, Grietje, Greta).
Catholic families often gave their children two or even three first names, so if you see a string of names like Johannes Gerardus Theodorus, you can make a bet that the family was Catholic.