PostScript is built-in to high-end printing hardware and PDF does a good job at encapsulating PostScript which gives you high reliability that the thing on the screen is going to print out the same way that it appears on the screen. Adobe has traditionally had a dominant role in both font (Type 1, OTF) technology and licensing and creative tools (Illustrator - a .ai file is a PDF) and so both the creation and consumption sides of the ecosystem have coalesced around a common format whose semantics carry through predictably (though not simply!) from one end to another.

What makes PDF particularly challenging is that there are so many broken PDFs out there which must be tolerated and so many legacy fonts, images and formats which have accumulated in the format over time - JPEG 2000 anybody?

Most complaints I see about PDF though are usually “why can’t it just wrap lines” and the answer is that there’s a zillion ways to do that and we’re supposed to be representing the output of that process as a visual artifact, not the input, as HTML does, because the use case is printing and stability of the output is non-negotiable.

Can you name a competing format that ended up being "better" than PDF? Not intending to say there is no such format. I'm genuinely curious.

XPS is better in many ways, apart from its obvious failure in the market.

XPS is wonderful but it arrived 20 years too late.

Because it became, as a descendent of Postscript, a pretty dominant standard for situations where you wanted to specify the layout.

There's certainly a lot of legacy embedded in PDF which doesn't help.

>Is the explanation really as lame as "They were there first and it stuck"?

I'm not sure they were first but they became dominant because... Adobe. And Adobe made it an open standard which pretty sealed the deal.

Because it is the only format with mass adoption that makes presentation reasonably stable. Plus it's the format with the only reasonable authoring tools.

Personally, I enjoy working with DeJaVu files very much but you only find those of pirated ebooks.

DjVu isn’t a vector format, so it’s not quite a replacement.

Why do you wince when you have to sign one?

As an engineer I can see why you would find the spec inelegant.

But as an end-user, using it to fill in forms couldn't be easier.

What do you use for form filling. During job applications last year nearly all the pdf forms were just images, or vector boxes that you couldn't fill ...

Acrobat Reader (free) has the "Add text" tool that lets you add text anywhere you want.

Similarly macOS Preview (free) has an identical "Text" tool to add text anywhere.

I've never checked other programs, but those are certainly the two default tools one would use with PDF's on Macs.