I can confirm the PDF is not present on OS X 10.9 Mavericks.

So it was added some time between 10.10 and 10.14.

It was almost certainly added around the hype in 2019.

2015-2017 and 2021-2022 were hype years. 2018-2020 was dead crypto winter.

On my Mojave machine the files modtime is “ Mon Aug 20 2018”! (Which seems to be straight from macOS, not the date of my install, since the modtime on other macOS system files varies widely)

That’s roughly the date they’d have done the full world build for the first non-beta release of Mojave based on its actual release date. It’s unlikely it was actually the date of creation

Agreed! But just pointing out they did this prior to the 2019 hype the parent poster mentioned

On mine, it's Jan 1 2020 (Big Sur, 11.7.4).

Others have confirmed to me that it wasn't in High Sierra (10.13) and shipped with Mojave in 10.14.0.