Spiritually a seal suggests hidden knowledge. Not all esoteric and occult information is available to everyone; such information is only entrusted to someone who has the courage to break the seal.
Psychological / Emotional Perspective:
When we dream of legal documents, and are particularly aware of the seal, it can indicate that a conclusion has been reached in waking life which is both binding and secret. To be breaking a seal indicates that we are possibly breaking a confidence or someone’s trust in us. In dreams, the possession of a seal gives us the authority to take responsibility for our own actions.
Everyday Material Aspects:
Historically, a wax seal confirmed authority and power. It was also a symbol of identity. Nowadays in dreams it is much more likely to signify legality or correct moral action.
Gender / Specific Meanings:
It has been suggested that in a woman’s dream a man breaking a seal suggests that she will lose her virginity or purity at some level. In his own dreams, it will suggest that he is aware of the seriousness of his actions.
You might also like to consult the entry for Wax as well as the information for Seal in Animals.