Thanks for reaching out. Reviewers don't need to have a CC subscription, they just need to have an Adobe ID which is free.
As mentioned in the thread shared earlier, they can create one and then just login when they receive the email or notification about the document to be reviewed.
You may also check out this help article for more information about it. Hope it helps.
"Does the client need to have Creative Cloud to access the review document sent?"
no! Just an Adobe Account one can set up for free.
( ACP )