Yes. Drawboard PDF is free.
Check out our blog post here: Drawboard PDF essentials now free
Drawboard PDF was also pre-installed on the Microsoft Surface Pro 4, Surface Book and Surface 3 devices manufactured before 2017. Drawboard PDF was never pre-installed on the Surface Pro 3, Pro 2 or RT.
You can purchase the Drawboard PDF PRO subscription in the app to get access to the PRO features. Click here: Drawboard PDF PRO: How to Purchase PRO?