I have an USB that is used by an application to sign files: the application uses the USB to generates some files.
What I want is to list the files inside the USB. The problem is that the USB is not showing on Windows explorer. There is no letter affected to the USB, and I can't affect a drive letter to it sing Windows Disk Manager.
What is the type of this USBs, and how one can access files inside them?
Thanks in advance for any clarification,
What you have is a Dongle. It's not meant to store files or to be mounted (at least in the standard sense).
On your computer there's a driver that understands how to communicate with the dongle, and retrieve data from it. This adds some physical security, as you need to USB itself to perform the signing (and you can't just copy it).
If you wanted to know more about your particular USB Dongle, you'd have to find documentation for it (if any), perform low level communications to the dongle, and possibly have some kind of security credentials to communicate successfully with it.