Well, from what i read so far, you have to renew every year to keep using the PRO features.
So after one year, you either can buy a new annual PRO license or the program will revert back to the FREE version.
Here is a answer directly from one of the VSDC team members from 2017:
https://forum.ddigest.com/f105/vsdc-pro-license-options-distinctions-97237.html#post595937