我只能在仿真器上查看PDF文件，而不能在Flutter应用程序的真实设备上查看

dependencies:
  flutter_pdf_viewer: ^1.0.0

import 'package:flutter/material.dart';
import 'package:flutter_pdf_viewer/flutter_pdf_viewer.dart';

class PdfViewerPage extends StatelessWidget {
  final String pdfUrl;

  PdfViewerPage({required this.pdfUrl});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('PDF Viewer'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Open PDF'),
          onPressed: () {
            FlutterPdfViewer.loadPDF(pdfUrl);
          },
        ),
      ),
    );
  }
}