Do people that are not Catholics that marry and divorce need to get an annulment when they decide to become Catholic? Can they use "Internal Forum" to bypass the annulment process or is it even applicable in this situation? Thank you.
A Catholic is bound to follow canonical form when getting married. For two non-Catholics, when they enter into a marriage it is presumed valid. If one (or both) of them was unbaptized it is a natural marriage, if they were both baptized then it is a sacramental marriage.
A natural marriage may be dissolved in favor of the faith if the person is converting (1 Cor 7:10-15). A sacramental marriage can never be dissolved and an investigation would be needed to see if there is any evidence that the marriage was sacramentally invalid from the start.
Because marriage is a public act it cannot be resolved via the so-called “internal forum” solution.