I really enjoyed working with the Preview team before I retired from Apple. My small group created a private framework that added "document reconstruction" to PDF documents: basically an inferred DOM based on whatever information (mainly geometric) we could use in the PDF document.

Our moment of fame game at WWDC 2009, when Bertrand Serlet talked about Snow Leopard during the Keynote. At around the 5:10 mark he talks about performance improvements to Preview. He then goes on to say "There are also lots of little touches. The one I like is about text selection in PDF files. .... In Snow Leopard, we have used a little bit of AI to infer the structure of the document...." (He then demonstrates intelligent selection across columns) [Applause from the audience]. (https://youtu.be/FTfChHwGFf0?t=306)

My colleague and I presented the proposal to add this "little bit of AI" to a small group from the Graphics and Imaging department. Bertrand was in attendance, and it was thanks to him that we joined G&I. They were a fantastic team to work with!