Sorry, there is currently no way to provide a custom thumbnail for document files.
Mitchell,
I get thumbnails of my PDFs in the Media Library (Imagemagick and imagick PHP plug-in are installed on the host server). But I do not get thumbnails of PDFs in your file list. I love it and want to stay with you, but I’d really love to see PDF thumbnails in the list, just as I do in my Media Folder.
Yes, I could look at adding that. Good idea.
There are several links in StackOverflow about this. PDF.js from Mozilla and something called GD is mentioned. I post list of old pdf versions of newspapers (with permission) and being able to simply drop a PDF in and have your wonderful plugin generate a thumbnail would be awesome. Definitely would add your extensions.
Yes, I’m certain it’s doable, and I’d make this a standard feature like the FFmpeg video thumbs are. Just the matter of digging in an doing it. It’s on the To-Do list now.