Can this film be applied to the exterior side of a window? Specifically a skylight? If so how well does it weather rain, snow, sunshine, etc?

This particular film is not designed for the elements, especially a skylight. We do have one exterior rated very effective solar film. It offers a 5 year warranty. https://www.decorativefilm.com/ultracool-s2060osw-outside-weatherable-heat-rejection-film