We have a quota on the number of documents you can create, after which you must subscribe. It's a very generous quota, but we still have a good number of people subscribing.
Our major income comes from larger corporate contracts with medium to large businesses, that deploy our product on-prem. Often these were people who used our SaaS product, liked it, and asked us to deploy it internally for their business. Much less hassle than running a company that's purely SaaS based, and more stable income!