Introducing PDFXKit – A Drop-In Replacement for Apple's PDFKit

"A drop-in replacement for Apple's PDFKit" is marketing speak approaching lying.

The combination (PDFXKit + PSPDFKit) is a replacement for PDFKit, not PDFXKit alone; PDFXKit is just a wrapper library around their commercial product PSPDFKit that gives it the same interface as PDFKit.

Because of that, the BSD licensed PDFXKit isn't worth anything without the commercial PSPDFKit.