var types() As String
types.append “public.image”
types.append "public.text"
types.append "public.rtf"
types.append "com.adobe.pdf"
types.append "com.microsoft.excel.xls" // Old Excel Format
types.append "org.openxmlformats.spreadsheetml.sheet" // New Excel Format
types.append "com.microsoft.word.doc" // Old Word Format
types.append "org.openxmlformats.wordprocessingml.document" // New Word Format
types.append "com.apple.iwork.pages.sffpages"
types.append "com.apple.iwork.numbers.sffnumbers"
types.append "com.apple.iwork.keynote.sffkey"

var picker as New UIDocumentPicker(UIDocumentPicker.ModeImport, types, True)
picker.Screen = Self
picker.shouldShowFileExtensions = True
picker.Present

// you need to keep picker in a property!