Download a file in Web Portal from FTP server

Hi everyone,

I need to download a file from an FTP server via the Web Portal (by clicking a button).
I'm trying to use Code Snippet node in Web Designer.
I tried downloading files using a System.Net.WebClient (C#) but the file download doesn't start and a "Loading Content" loading screen remains.

Here is the code used:
using (var client = new System.Net.WebClient()) {
    client.Credentials = new NetworkCredential("UserName", "Password");
    client.DownloadFile(filepath, "file.pdf");
}


Any suggestion?
How can I download file from FTP server via Web Portal?