Generally test and development servers do not have to be licensed, as long as they are used to develop and test the integration of PDFreactor into your application and not for the creation of PDF documents that will be used in production. Customers who have a valid PDFreactor license with an active 1 Year Support & Maintenance subscription are welcome to request a special PDFreactor license for test, development purposes here. They will receive a full license key which is valid during the subscription period. Renewing can be done as often as required. You are not allowed to use your unlimited full license key on your test and development servers.
Staging and preproduction environments which are used in the content management sense - that is in the sense that PDF documents generated on this machine will be used in production - require a production license. If the latter does not apply to your staging or preproduction environment you can of course use the development key for those environments.