There is a Calibre forum here that would provide a better chance that your questions
will be answered to your satisfaction.
You don't need to do anything to Calibre for it to recognize when a device becomes
connected to your PC, through an USB port. All you need to do is have Calibre running
then plugin your USB cable to your device. This assumes that you are running an
operating system (OS) that itself recognizes when a USB device is connected.
Assuming you mean that you went to "the containing folder" and dragged the file that
was your newspaper feed, in a format that your Libre Pro and its firmware version
supports into the drive letter that your OS assigned to your device, then it should be
readable on your device. If the file in the folder is not one that the Libre supports,
Calibre can convert it to one like .epub that it does support.