1. A door may represent an opening to a new phase of life or a possible new development - either in your external circumstances or in yourself.
2. It may symbolize an invitation to enter the not-yet-explored parts of your psyche, with a view to bringing these under conscious control.
3. If someone/something is on the other side of the door, this probably means you need to let something come out of your unconscious into your conscious mind.
4. The symbolism may be that which Christians apply to the Christ: the way to 'salvation' - that is, healing and wholeness. (Compare St John’s Gospel 10:9: 'I am the door. By me, if anyone enters in, he shall be saved’.)
5. A closed door may symbolize A ‘no-go’ situation. You need to determine whether the impasse is unavoidable and therefore to be accepted (because, for instance, you have been pursuing a path that is out of keeping with your deepest values or needs) or one that you have artificially made for yourself (as a consequence of irrational guiltfeelings and anxiety, for instance) and can therefore remove by an act of will - though it may require a lot of preparatory work by way of investigating the (partly) unconscious psychic processes that have constructed the obstacle.
Since a Door is both an exit and an entrance, and can deny passage as well as welcome a person through its threshold, its symbolism is entirely dependent on its working status. Is the dreamer locked out, and refused (therefore,) passage into potential change; or are doors opening automatically, simply because of the fervor and zeal of the dreamer’s self-confidence? Accordingly, we need to analyze our relative position to the door and any and all characters (or objects) which appear on either side of the door, for the legitimate meaning of our (perhaps shifting) state of mind.