Solved! Go to Solution.
While this is true, you can use the free version of Mathcad Prime 8 (latest version) to open documents produced in Mathcad Prime 5.
Edit: Quick note that Mathcad Express (free version) should not be used for commercial purposes, though that restriction doesn't apply to the 30-day trial licence. If you need it for commercial purposes, please contact PTC to purchase a licence.