For future reference:

"DocumentUltimate" watermark means your license key is not accepted and you are in unlicensed mode. For example it would appear if you updated the product (new DLLs) when you are still using your old license key with it.

We usually change license keys when we release major version (e.g. from 3.0 to 4.0).
So when updating your version you should also check your license key here (usually not required for minor versions e.g. from 3.0 to 3.5):
https://www.gleamtech.com/upgrade

We also announce in the version history when the license key are changed.

Depending on your purchase date, you may already be eligible for a free key for the new version. You can check this availability by entering your existing key on the above Upgrade page. If you are not provided with a free key, then you can buy a new key with the discounted upgrade price on the same page.

License keys are bound to a version range.
So for example if you have v2.x license key, you can't use it with v4.x product.

Note that you can continue to use v2.x license key with v2.x product, if you don't want to update the product.