If I purchase a monthly plan am I committed to a year of payments or can I cancel at any time without further payments?
There are different plans
"Annual (paid monthly)" - you must pay for a year. If you cancel early you must pay a cancellation fee. There is a 50% discount, so you pay only half the rest of the year. At the end of the year it renews for another year, forever until you cancel.
"Monthly" - costs more but you can cancel any time with no fee.
Adobe's two types of plans are Monthly (month-to-month) or Annual (yearly). Here's a full comparison of the two options.
The terminology can be confusing because in both cases, you can pay each month... But in the first case (Monthly), there is no 12-month commitment and you can cancel at any time with no early termination fee, although the per-month cost is higher.