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 fairly unrestricted personal and commercial use.

You are also allowed bundling Page Builder with your own themes, provided the theme is licensed under GPL. You’re even allowed selling 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, I’d suggest just encouraging your users to install Page Builder from the WordPress plugin repo. This will ensure they stay up to date with the latest version of Page Builder. It’s an actively developed plugin with almost weekly updates and bug fixes.