It depends on how and what you use, you either buy a version out right and that is it. Or buy maintained where you pay a fee per year to keep updated with bits and bobs or the rental of a rolling upgrade.
Can you still buy it outright? If so, you be able won’t be for long.
The way Adobe works, as an effective monopoly on an entire industry, you’ll be increasingly unable to do that. They add features in that make it increasingly backwards-incompatible, so as to force everyone onto the subscription model. Once they feel they’ve achieved that, expect subscription costs to sky-rocket.
As someone who bought a full version of CS6, which now won’t open CC indesign files, thus being forced onto CC, I feel like I’m effectively paying for everything twice!
Adobe are ****s!!!