In “normal” speech – to say that one “sees” something is a very general way of saying that: The image of some “thing” is registered by the visual sensory apparatus – while, to “watch” something means: To be focused on that “thing” which one sees (but is usually something which is moving.)
However, when using these two verbs to talk about “Movies” or “Films” (whichever term you prefer) – they have slightly different meanings…
To “See A Movie” is the phrase used to refer to the event of actually going to the theater or cinema to view the movie in that facility…
To “Watch A Movie” is the phrase used to refer simply to the act of viewing that movie (wherever it may be.)…
Also Note:The phrase, “To see a movie” is always used with either “going to”, “off to” or some other verb phrase, putting the subject in the future – and, thus, acting as an infinitive phrase.
To say that one “has seen” a movie, carries the natural meaning one would expect from a sentence in the present perfect tense.
In other words – that it has actually happened at some point in past – when it happened is either not known or not important – and that the action has an affect on the the present state… (because one can not “un-watch” a movie.)
Have An Excellent Day!