Below i will share a fix on how to view PDF documents in Windows Explorer Preview.
1- Open Control Panel > search Folder Options > click Restore Defaults under each of General, View, and Search tabs.
2- Search for Internet Options under Control Panel > click Advanced tab > Reset (you might try resetting IE without selecting “Delete personal settings” first).
3- Launch Reader > click Edit > Preferences > General > click Select As Default PDF Handler>OK
4- Reboot the machine.