If you get that WPBakery page builder free with porto theme then porto theme author paid for that no worry about that.
You can follow this link for that plugin as in bundle plugin
As you have received the WPBakery Page Builder plugin from the theme bundle. Theme Bundled plugins do not have their own licenses. This means they cannot be activated mean registered for updates. So you can safely ignore any plugin activation/registration messages and WPBakery Page Builder plugin will work fine without activated mean registered.
If the theme author does not update the page builder, how do I keep up with the page builder and theme updates? We re-purchased the Theme Bundle yesterday, but not sure if it will overwrite the content that is already on the website.