Make sure the following things:
1. The Shell Extension component in Foxit Reader was installed. Navigate to C:\Program Files (x86)\Foxit Software\Foxit Reader\Shell Extensions, see if there are two dll files and one exe files. If they appear, the component was installed. Otherwise, Foxit Reader needs to be reinstalled by checking "Shell Extensions" option during Installation Wizard.
2. In the Windows File Manager, open the Folder Options, make sure the option Always show icons, never thumbnails option is off , and the option Show preview handlers in preview pane is on.
3. In the Windows File Manager, change the view layout to Medium icons or larger
If info above makes no difference, please refer to the link to register plugins for previewer again.