There's nothing special about PDF. Only reason PDF is useful is because it's easy to convert to/from Postscript and Adobe was pushing out a free viewer for PDFs but not Postscript files. That, and the difference in fees they chose to charge on the formats.
> there was a period of time when I thought PDF’s days were numbered
And indeed you are correct! A time shall arise, sooner or later in the future, a moment when the last PDF file is created, as well as a moment when a PDF is consulted for the last time. Depending on your definition of format obsolescence, this might be well beyond its expiry date, or it might actually mark the moment of death.
(Let’s forget that the Apple lineage of OSes derived from Display PostScript-using NeXTstep such as OS X [latterly macOS], iOS, iPadOS, watchOS and tvOS all use PDF as a mechanism for drawing primitive sources onto the screen.)
Anyway... after that long preamble, statements like these remind me very much of Goldfinger’s famous quote, and in honour of Sean Connery’s passing yesterday I will allow myself to elucidate:
Bond: “Do you expect me to talk?”
Goldfinger: “I expect you to die!”
The latter being a very reliable expectation, but one that can sometimes take a lot longer to come true than the utterer might have in mind when they make the assertion.