```dart title="Dart" import 'package:kreuzberg/kreuzberg.dart'; Future main() async { // Custom document extractors cannot be implemented in Dart. Creating a // PDF metadata extractor would require implementing the DocumentExtractor // trait, but flutter_rust_bridge does not generate the // createDocumentExtractorDartImpl factory function. // // Implement the PDF metadata extractor in Rust and register it via a // Rust shim crate that links kreuzberg before the Dart host loads the // dynamic library. } ```