Could this potentially become a Full version Document Management System with Login, User Permission and Grouping, etc :)
Yes. It already has single-user login, but with multi-user/permissions coming soon. Because Files app reads existing file structure and does not use a database, there would be some limitations compared to other apps that also manage the file system.
mrSLK wrote:and is there a way to do a preview of pdf files ?
Do you mean preview images from the PDF first page for the layout? There is a way by using ImageMagick, but this is only available on some hosts or if you run your own server (with SSH access).
Personally, I'm not a fan of PDF thumbnails, as mostly it's just some downsized unreadable text that makes all the thumbnails look identical. It would only be useful if the PDF's have some graphic/image on the cover.