> To be fair, I think this feature is not built into dired either and would require an additional package[2] It is not part of Dired but it is part of Emacs, s

> To be fair, I think this feature is not built into dired either and would require an additional package[2] It is not part of Dired but it is part of Emacs, so it works out of the box. For example, in plain vanilla Emacs, if we type C-o on a PDF file displayed in Dired, it opens up the PDF file in a split window using doc-view. Similarly, if I type C-o on a PNG file, it opens up the PNG file using image-mode in a split window. So you're right that this isn't part of Dired but it is part of Emacs, so all of this works out of the box in vanilla Emacs with zero customisations.