The .fzip file is a Foxit add-on package format. It can only be recognized by Foxit applications. We cannot double-click to open .fzip file directly, but we can install the .fzip file from within Foxit PDF Reader.
Open Foxit PDF Reader, navigate to Help menu, click on Foxit Plug-ins, click on Install Plugins.
Navigate to the location folder you downloaded the FZIP Plug-in to, choose FZIP files from the dropdown menu, select the FZIP file and click Open.