There’s one most likely choice for the origin and application of this transparency, and a second somewhat less likely one.
The likeliest (because of the tape on the edges) is that this was a transparency intended for use on an overhead projector (these were the commonest way to do presentations that involved writing or drawing, live for a large group), and would have been part of a presentation, either about spaceflight in general, about the Apollo program, or about Earth (from a NASA standpoint). This film piece would have been simply laid on the projection glass, and the optics of the projector would put it on the screen. Overhead projection is the most likely because by the 1970s, 4×5 format film projectors were already a rarity (35mm and medium format projectors were still common).
Next most likely is that it was a promotional piece, either intended for sale in a gift shop (to be viewed in a light box or incorporated into a lamp shade or similar, perhaps) or for direct sale to the public as part of NASA’s self-promotion programs.
It’s very unlikely that it’s an original, most tellingly because Apollo never carried large format camera gear — they carried Hasselblad cameras, shooting 6×6 cm format (56mm square actual image area) on 70mm double perforated film; if this were an original, it would be smaller than it is and have perforated edges. That makes it a copy, and copies weren’t generally used for science — but iconic images like that one went far to promote NASA and their scientific missions to the general public.