[e1ven]

That's exactly what I like about it. My ideal PDF is essentially a PNG file with selectable/searchable text.

It's a great WORM format. Every added feature makes it worse.

[jolmg]

Why is it desireable for it to not be machine readable? What could possibly be the advantage in that?

[e1ven]

Because I don't want anything to try to reflow the text, or adjust the kerning, or modify to use system fonts.

There are great systems for those already.

When I want a PDF, it's because I want a format that I know is always going to look the same.

A PDF is a great archive format. It's perfect for a scan of a document, or a printout.

I never want my viewer to add anything to it, I never want it to detect anything, I never want it to adjust anything.

Just render it exactly the same way, every time.

[jolmg]

One thing doesn't imply the other. The format could be machine readable and still be pixel-perfect consistent. It could also allow reflowing, adjusting the kerning, or use system fonts even if it's machine unreadable.

[Spooky23]

It is machine readable, just not readily machine malleable.

I worked on a project where we were digitizing and cataloging various records. It was less challenging to do this with papers from the British colonial administration from the late 1700s, than to decipher certain 1980s documents written with a defunct word processor. PDF is a compromise that helps address that issue.

I would not recommend maintaining your general ledger in a PDF. But an annual report that may be referenced for decades is a great example of why a PDF is a useful format.