FilePickeriOS.cs

public void DidPickDocumentPicker (UIDocumentMenuViewController documentMenu, UIDocumentPickerViewController documentPicker)
		{
			documentPicker.DidPickDocument += DocumentPicker_DidPickDocument;

			UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewController (documentPicker, true, null);
		}

		void DocumentPicker_DidPickDocument (object sender, UIDocumentPickedEventArgs e)
		{
			var securityEnabled = e.Url.StartAccessingSecurityScopedResource ();

			System.Diagnostics.Debug.WriteLine (e.Url);

			var doc = new UIDocument (e.Url);


		}

		public void Dispose ()
		{
			
		}

		public async Task<byte[]> GetByteFile ()
		{
			var allowedUTIs = new string[] {
				UTType.UTF8PlainText,
				UTType.PlainText,
				UTType.RTF,
				UTType.PNG,
				UTType.Text,
				UTType.PDF,
				UTType.Image,
				UTType.UTF16PlainText,
				UTType.FileURL
			};

			UIDocumentMenuViewController importMenu =
				new UIDocumentMenuViewController (allowedUTIs, UIDocumentPickerMode.Import);
			importMenu.Delegate = this;

			importMenu.ModalPresentationStyle = UIModalPresentationStyle.Popover;

			UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewController (importMenu, true, null);

			UIPopoverPresentationController presPopover = importMenu.PopoverPresentationController;

			if (presPopover != null) {
				presPopover.SourceView = UIApplication.SharedApplication.KeyWindow.RootViewController.View;
				presPopover.PermittedArrowDirections = UIPopoverArrowDirection.Down;
//				presPopover.SourceRect = ((UIButton)s).Frame;
			}

			return new byte[0];
		}