How can you cryptographically sign (ECDSA) a PDF on iOS with Apple's PDFKit and save it in the PDF file? From the framework intro one would expect to find most of the PDF spec features implemented, but I struggle to find anything about cryptographic signatures (non-graphical). So, did I miss something, is there some undocumented functionality, or how would you approach this?
I've experience with manipulating and signing PDF documents in Java, but lack experience in iOS/Swift.