SFTP, which stands for SSH File Transfer Protocol, or Secure File Transfer Protocol, is a separate protocol packaged with SSH that works in a similar way over a secure connection. This activity can be used to retrieve a string of files available on a server.
You have to mention the key path which is a private key.
After you get the output you can split the string by new line.
Note : You need to place the winscp.dll file in your activity packages folder after you install this package.
Download the link of the above mentioned dll : https://www.dllme.com/dll/files/winscpnet_dll.html