To install the full version please do the following:
1.- Download the full version of the plugin. You can find your download link in the receipt that you received after purchasing or you can log into your account and get the license from there https://pdfimporter.rednao.com/checkout/purchase-history/
2.- (Optional) if you have the free version of the plugin, make sure you deactivate it before installing the full version.
3.- Go to your WordPress dashboard and click in Plugins/Add ...