Author-it has developed and released Author-it Web Help based on the Ext JS Commercial License Agreement.
If you're customizing Web Help templates and/or themes and don't need to modify any Javascript (JS) files, you won't require an Ext JS developer license, and you can customize Web Help templates and distribute the Web Help with no problems.
However, if you do need to modify any Javascript files, Author-it is not able to offer any support. In this case, it's your legal responsibility to determine whether you need to purchase a developer license for the Ext JS framework from Sencha.