I've run into what appears to be a bug in PDFKit's radio button serialization. When creating a radio button group with PDFAnnotation, only the first annotation added via page.addAnnotation() gets a correct /AS entry in the written PDF — all other annotations always get /AS /Off, regardless of buttonWidgetState. Minimal reproduction func makeRadioButton(optionId: String, isSelected: Bool) -> PDFAnnotation { let ann = PDFAnnotation(bounds: CGRect(x: 0, y: 0, width: 20, height: 20), forType: .widget, withProperties: nil) ann.widgetFieldType = .button ann.widgetControlType = .radioButtonControl ann.fieldName = "Choice" ann.buttonWidgetStateString = optionId ann.buttonWidgetState = isSelected ? .onState : .offState return ann } let pdf = PDFDocument() let page = PDFPage() pdf.insert(page, at: 0) // Intend to select B page.addAnnotation(makeRadioButton(optionId: "A", isSelected: false)) page.addAnnotation(makeRadioButton(optionId: "B", isSelected: true)) page.addAnnotation(makeRadioButton(optionId: "C", isSelected: false)) _ = pdf.dataRepresentation() // Result: /AS is /Off for all three — B is not selected in the PDF What I observed Selecting A (first annotation added): /AS /A written correctly works Selecting B or C: /AS /Off for all buttons Additionally, dataRepresentation() corrupts the in-memory state as a side effect: buttonWidgetState of the selected annotation is .onState before the call and .offState after. Root cause During serialization, dataRepresentation() internally calls setButtonWidgetState:.onState on each annotation in turn to generate appearance streams. This triggers PDFKit's radio-group exclusivity logic, which silently clears all other annotations — so by the time /AS is written, only the first annotation's selection survives. Workaround It took a while to track this down, so I'm documenting the workaround here in case it helps others. Add the annotation that should be selected first via page.addAnnotation(): // Add selected annotation first page.addAnnotation(makeRadioButton(optionId: "B", isSelected: true)) page.addAnnotation(makeRadioButton(optionId: "A", isSelected: false)) page.addAnnotation(makeRadioButton(optionId: "C", isSelected: false)) Tested on macOS 26.3 / Xcode 26.3. Filed as Feedback FB22167174. Full code including workaround is here: radio_bug_swift.txt Has anyone else hit this? Is there a cleaner method I'm missing?