Exactly. PDFs are documents, not images. Just because ImageMagick can convert PDFs into images doesn't make them images.

Every image viewer on Earth excludes DOCs and PPTs by default, but nobody complains about that.

I recall at least one vector drawing program offering PDF as target, and this being expected in some print shops, so yes, in some cases, PDFs can be images.

PDF is a weird format with a bunch of disjoint use cases.

GIMP offers ASCII art as a target, and that's expected by line printers/teletypewriters; does that mean TXTs can be images?

That’s a weird edge case. It’s images to us nerds and hackers but it’s certainly not images to anyone in print. Where as PDFs were used to send final magazine pages (for example) which were ready for print.

(Source: I worked for a publishing company in the 90s)

Yeah, you just described how too. KDE used to thumbnail txt files with a portion of their actual text.

Still does.

Dolphin → Settings → Configure Dolphin… → General → Previews

I see; I mostly used KDE in the 3.x days, back when Konqueror was the file manager and Webkit was still a fairly young KHTML fork.

Konqueror and Dolphin use the same kpart under the hood for directory display.

Konqueror → Settings → Configure Konqueror… → File Management → General → Previews leads to the same configuration dialog.

I think the reason for that is more to do with history than anything. The original intended purpose of PDFs were to be a print quality final layout.

That’s not so much the case these days and Word documents / PowerPoint presentations have supported embedding fonts too so they’ve drifted a little into PDFs territory. But from a generalised and historic standpoint: Word documents were for editing and PDFs were for printing.

In my experience of academia, using PDFs as an image format is extremely common for sharing plotted data. The only common alternatives are (E)PS and PNG which are much worse.

You can use PDFs in Xcode. Instead of using a single image for all the different resolutions and polluting your fs is actually really nice to have a single file with preview