The Files module does have a Preview feature for some types of files. But, in my opinion and for my purposes, it is not very user friendly. Even pdf files as small as 10 megs get a warning message (apparently from Google, a rip-off company which I really cannot stand. Haha.) which says: "Oooops - too big for a preview."

Video and Sound files have no preview at all and the user gets an unfriendly message which states: "Preview not available."

I just need to be able to add a single image before the text or the video or the sound file. This is the usual and universal convention used in billions of blog posts and web sites across the internet.