With Perpetual license you will get a free 1-year Update period, which entitles you to update your software to any new versions released in that year. After that year, if you want to keep receiving software updates, you can optionally renew your Update Plan, by paying 20% of the user license amount. In any case, your license will stay valid forever and Output Books will stay fully functional, even after your Update Plan has expired. The versions older than 2 years will stop getting updates as it is harder to maintain. So it is recommended to update once in 3 years.