func didPickDocument(document: Document?) {
    if let pickedDoc = document {
        let fileURL = pickedDoc.fileURL
        let data = try Data(contentsOf: fileURL)
   class ViewController: UIViewController, DocumentDelegate {
       override func viewDidLoad() {
         super.viewDidLoad()
     @IBAction func actionButtonTapped(_ sender: Any) {
        let documentPicker = DocumentPicker(presentationController: self, delegate: self)
       documentPicker.displayPicker()
/// callback from the document picker
func didPickDocument(document: Document?) {
    if let pickedDoc = document {
        let fileURL = pickedDoc.fileURL
        /// do what you want with the file URL
        print(fileURL)
        let data = try Data(contentsOf: fileURL)