There’s a few ways to transfer files between Linux machines though one of the easiest is to use SCP (secure copy protocol), to my knowledge all major Linux distributions support SCP so this short tutorial shouldn’t be limited to a single distribution.
First you’re going to need to upload your recipients private key to the machine you want to transfer files from, on Windows I’m going to use a program called WinSCP, once uploaded you need to use chmod command (example below) to secure the key so only the owner is able to use it.
sudo chmod 600 yourprivatekeyYou can use the command below to ensure the chmod worked, you may find a chmod calculator website useful.