A FileCloud admin having access to the FileCloud admin portal and can use some API endpoints to access any arbitrary file in the underlying file system.
This requires the FC document convertor to be configured and functional in the same machine.
This has been fixed in FileCloud versions 184.108.40.20692 and later.
If you are using FileCloud on premise installation, please update to the latest version.
If you are using FileCloud online, your site has already been updated to the latest version.