With the perpetual plan/license, you own the software forever and have free minor updates within the specific version that you purchased. However, you might need to pay for major upgrades.
For example, if you buy PDFelement 9 perpetual plan now, you can use version 9 forever and you will also enjoy free updates from V9.1.X to V9.2.X. But you might need to pay for major upgrades to V10.X.X. Normally we will provide a special discount for old users to upgrade when the new major version is available.
Please do not worry, no matter whether you decide to pay for a major upgrade or not, you will always enjoy technical support with the lifetime plans/license.