there is a lot of good info in replies posted here, and a lot if mistakes and misapprehensions. Nobody can “go get an annulment”. If an individual feels his marriage was invalid for any reason, he goes to his pastor, who refers him to the diocesan marriage tribunal, who will gather all the facts, make an investigation. If the marriage was in fact invalid for any of a number of reasons, they will issue decree of nullity, approved by the bishop.
Repeat, repeat, repeat, everyone’s situation is different. It is nearly impossible to make an accurate assessment of a hypothetical case. Go to your pastor and lay the facts before him - all the facts. Get his recommendation. If your pastor seems uninformed, ask him to make an appointment with you to talk to someone from the tribunal.
If anyone here is a catechist for RCIA, make sure there is a pastor person on your team, the deacon or priest, to discuss marriages with each catechumen or candidate and investigate their status before they begin preparation for the other sacraments. As a lay person, do not try to give advice by yourself.