qBittorrent official forums

When I add a torrent to qbittorrent, I get a screen as shown in the attachment

Is there a way to get the folder/file names and the related file size as a text file without actually downloading the entire torrent file?

Of course. The information you want is literally inside the .torrent file. However, magnet links don't have these informations. With magnets, you will download the .torrent from existing other peers first.