Doc customizer does not show the preview of the document on your site, however if I modify some settings it has effect on the printed documents.
There may be a plugin or theme conflict on your site.
Please chose a default theme (e.g. twenty seventeen), and disable all your plugins, except WooCommerce, Filogy and Filogy Framework plugins, and check if preview is displayed or not in Doc Customizer.
If it is working without problem, then activate your other plugins one by one, and find that plugin that causes the problem.