While you can see some judo techniques used in hapkido, there are a couple of big differences between the two. For starters, judo places its focus on throws and pins and you can’t see striking in judo. Hapkido, on the other hand, uses leg and hand strikes.
Another major difference is that judo is an Olympic sport and has thousands of tournaments held worldwide. Competitions in hapkido are rarer, not to say non-existent, but they are nowhere close.
Sparring is also a major difference between judo and hapkido. Hapkido isn’t a martial art that can pride itself in sparring, and a lot of hapkido classes focus on demonstrating the techniques, rather than sparring. This is a major advantage of judo since its techniques are proven to work against opponents that are resisting.