Swift PDFKit handle annotation widget change?

Question

Is it possible to handle on change in swift pdf annotations? I would like to highlight the fields that need to be filled and then unhighlight when they have been filled.

   pdfView.document = PDFDocument(url: url!)
                    for index in 0..<pdfView.document!.pageCount{
                            if let page = pdfView.document?.page(at: index){
                                let annotations = page.annotations
                                for annotation in annotations{
                                    print("Annotation Name :: \(annotation.fieldName ?? "")")
                                    annotation.backgroundColor = .opaqueSeparator
                                    switch annotation.fieldName {
                                    case "Customer":
                                        annotation.widgetStringValue = "Customer"
                                        annotation.backgroundColor = .tertiarySystemFill
                                    case "Customer Email":
                                        annotation.widgetStringValue = "Customer Email"
                                        annotation.backgroundColor = .tertiarySystemFill
                                    default:
                                        annotation.widgetStringValue = ""
                                    }
                                    annotation.onChanged{ value in
                                        annotation.backgroundColor = .opaqueSeparator
                                    }
                                }
                            }
                        }

Annotations do not have a onChange or onChanged, what is the best way to go about this.

Thanks for any help!!