OK, so as I commented above. You cannot use WinSCP to decrypt the files.
That information is from the Host server's application User Guide (GoAnyWhere MFT)
Where does your quote come from? WinSCP cannot decrypt file encrypted with an arbitrary encryption your server happens to use.
Below is the information within the application documentation.
•Encrypted folders for protecting files at rest using AES 256-bit encryption
Can you please elaborate on the "remote server's file encryption key". What kind of file encryption is that?
I have a batch file that downloads a file from another server. My question pertains to how to include the remote server's file encryption key into my batch file command line, so that when WinSCP completes the download the file will be de-decrypted.