@andybaio @mmasnick
From a few min of searching: VirtualScanner is a demo project from the Apple developer docs that shows how to implement a scanner driver.
https://developer.apple.com/library/archive/samplecode/VirtualScanner/Introduction/Intro.html#//apple_ref/doc/uid/DTS40011006-Intro-DontLinkElementID_2

That project uses embedded dummy images to simulate the scanner input. That’s what the PDF is doing there.

Not sure why VirtualScanner is bundled with macOS, but odds are it’s for testing / troubleshooting. Combine with this from @danstill@mastodon.social, and you can imagine how the PDF ended up in there: https://mastodon.social/@danstillman/110149897062210210