Page Builder is licensed under GPL 3.0. For full details of the license, you can read through
license.txt in the plugin folder. The GPL license allows for relatively unrestricted personal and commercial use.
You are also allowed to bundle Page Builder with themes you’ve authored, provided the theme is licensed under GPL. You’re even allowed to sell your theme.
If you want to sell your theme on ThemeForest, though, you’ll need to ensure that you select the GPL licensing option. Their standard license is not GPL compatible.
That said, we suggest encouraging your users to install Page Builder from the WordPress plugin repo. Doing so will ensure they stay up to date with the latest version of Page Builder. It’s an actively developed plugin with regular updates and bug fixes.