Everything described in these docs so far is in the free plugin, and it stays free. Quotly Pro is a separate add-on you install next to it.
Pro is a normal plugin zip. Upload it under Plugins, Add New, Upload Plugin, and activate. Keep the free plugin active, since Pro attaches to it.
Pro does not unlock code that was already sitting there. The Pro features ship in the add-on itself, which is why the free plugin has nothing switched off inside it.