Just adding to this problem. I'm confused by Apple's documentation for PDFOutline. It says: "The index of the outline object is relative to its siblings and from the perspective of the parent of the outline object. The root outline object, and any outline object without a parent, has an index value of 0." So that suggests that Outline objects added to the root Outline should have a non-zero index. But, when I try to add the first child with an index of 1, I get an NSArray Beyond Bounds error.

Quinn, thanks for your reply. Yes, I'm just building this for myself, but ideally I'd like to produce something that others can follow the steps of. Can you think of a better way of achieving the end result? As said, I tried AppleScript applications, but editing the Info.plist would always break the app. (No Entry sign.)

Even python 2.7 is still there!

Have you reset your NVRAM? I believe the option to chime or not is stored there. If a reset still keeps the chime, then you'll need to set it manually: sudo nvram StartupMute=%01

There isn't really a 'bank' of examples. Places like the Big Nerd Code Ranch have Xcode tutorials for creating apps that display PDFs using PDFView. Most of the original Quartz coding books were written before PDFKit was introduced, so use CGPDFDocument instead of PDFDocument, etc.I've produced a suite of python scripts that use PDFKit to do pretty much everything that PDFKit can do. As well as being functional, they're designed to be exemplars of how PDFKit works. If you know Swift, and are working in Xcode, then it should be easy to translate to Swift. On github, find /benwiggy/PDFsuite

Since no one else knows how to create an app that passes quarantine: the answer seems to be "No". Every app is suspicious, unless you pay Apple.