The easiest solution is going be to copy the file from the FTP site to your local C drive, edit it with the appropriate application, and then use the explorer to copy it back.
The Windows explorer knows how to "speak FTP", but most apps only "speak file I/O" to a drive letter (C:\Data) or a UNC path (\\servername\sharename). It's different API calls.
There appears to be a product named NetDrive that can serve as a translator between file I/O and FTP. I have not tried that.
https://superuser.com/questions/96876/how-do-i-map-an-ftp-site-to-my-computer-as-a-drive-letter
Office apps don't know what to do when Explorer tells them to open an FTP location.