使用flutter_pdfview包。
1.在Android清单中添加权限

<uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

1.在pubspec.yaml中添加依赖项

dependencies:
  flutter:
    sdk: flutter
  flutter_pdfview: ^1.0.1
  http: ^0.12.0+4
  path_provider: any
  permission_handler: 4.4.0 //For asking permission to load the pdf

1.然后使用PDFView
完整代码：

import 'package:flutter/material.dart';
import 'package:flutter_pdfview/flutter_pdfview.dart';
import 'dart:io';
import 'package:http/http.dart' as http;
import 'package:path_provider/path_provider.dart';
import 'package:permission_handler/permission_handler.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String urlPDFPath = "";
  bool exists = true;
  int _totalPages = 0;
  int _currentPage = 0;
  bool pdfReady = false;
  PDFViewController _pdfViewController;
  bool loaded = false;

  Future<File> getFileFromUrl(String url, {name}) async {
    var fileName = 'testonline';
    if (name != null) {
      fileName = name;
    }
    try {
      var data = await http.get(url);
      var bytes = data.bodyBytes;
      var dir = await getApplicationDocumentsDirectory();
      File file = File("${dir.path}/" + fileName + ".pdf");
      print(dir.path);
      File urlFile = await file.writeAsBytes(bytes);
      return urlFile;
    } catch (e) {
      throw Exception("Error opening url file");
    }
  }

  void requestPersmission() async {
    await PermissionHandler().requestPermissions([PermissionGroup.storage]);
  }

  @override
  void initState() {
    requestPersmission();
    getFileFromUrl("http://www.africau.edu/images/default/sample.pdf").then(
      (value) => {
        setState(() {
          if (value != null) {
            urlPDFPath = value.path;
            loaded = true;
            exists = true;
          } else {
            exists = false;
          }
        })
      },
    );
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    print(urlPDFPath);
    if (loaded) {
      return Scaffold(
        body: PDFView(
          filePath: urlPDFPath,
          autoSpacing: true,
          enableSwipe: true,
          pageSnap: true,
          swipeHorizontal: true,
          nightMode: false,
          onError: (e) {
            //Show some error message or UI
          },
          onRender: (_pages) {
            setState(() {
              _totalPages = _pages;
              pdfReady = true;
            });
          },
          onViewCreated: (PDFViewController vc) {
            setState(() {
              _pdfViewController = vc;
            });
          },
          onPageChanged: (int page, int total) {
            setState(() {
              _currentPage = page;
            });
          },
          onPageError: (page, e) {},
        ),
        floatingActionButton: Row(
          mainAxisAlignment: MainAxisAlignment.end,
          children: <Widget>[
            IconButton(
              icon: Icon(Icons.chevron_left),
              iconSize: 50,
              color: Colors.black,
              onPressed: () {
                setState(() {
                  if (_currentPage > 0) {
                    _currentPage--;
                    _pdfViewController.setPage(_currentPage);
                  }
                });
              },
            ),
            Text(
              "${_currentPage + 1}/$_totalPages",
              style: TextStyle(color: Colors.black, fontSize: 20),
            ),
            IconButton(
              icon: Icon(Icons.chevron_right),
              iconSize: 50,
              color: Colors.black,
              onPressed: () {
                setState(() {
                  if (_currentPage < _totalPages - 1) {
                    _currentPage++;
                    _pdfViewController.setPage(_currentPage);
                  }
                });
              },
            ),
          ],
        ),
      );
    } else {
      if (exists) {
        //Replace with your loading UI
        return Scaffold(
          appBar: AppBar(
            title: Text("Demo"),
          ),
          body: Text(
            "Loading..",
            style: TextStyle(fontSize: 20),
          ),
        );
      } else {
        //Replace Error UI
        return Scaffold(
          appBar: AppBar(
            title: Text("Demo"),
          ),
          body: Text(
            "PDF Not Available",
            style: TextStyle(fontSize: 20),
          ),
        );
      }
    }
  }
}

您可以使用flutter_cached_pdfview
这是一个超级的flutter_pdfview
得到了很多方法，以帮助你更快地与pdf工作
这是一个从URL查看pdf并缓存它的示例

PDF().cachedFromUrl('http://africau.edu/images/default/sample.pdf'),

它具有flutter_pdfview的所有功能
看一看https://pub.dev/packages/flutter_cached_pdfview

我一直在寻找解决这个问题的方法，我尝试了前面的答案中提到的，我没有得到一个很好的结果，在搜索和尝试了几个库后，我找到了一个最初对我有效的，我希望它能帮助你To you too syncfusion_flutter_pdfviewer

import 'package:flutter/material.dart';
import 'package:syncfusion_flutter_pdfviewer/pdfviewer.dart';

void main() {
  runApp(MaterialApp(
  title: 'Syncfusion PDF Viewer Demo',
  home: HomePage(),
 ));
}

 /// Represents Homepage for Navigation
 class HomePage extends StatefulWidget {
  @override
  _HomePage createState() => _HomePage();
 }

class _HomePage extends State<HomePage> {
final GlobalKey<SfPdfViewerState> _pdfViewerKey = GlobalKey();

@override
  void initState() {
    super.initState();
  }

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(
     title: const Text('Syncfusion Flutter PDF Viewer'),
    actions: <Widget>[
      IconButton(
        icon: const Icon(
          Icons.bookmark,
          color: Colors.white,
          semanticLabel: 'Bookmark',
        ),
        onPressed: () {
          _pdfViewerKey.currentState?.openBookmarkView();
        },
      ),
    ],
  ),
  body: SfPdfViewer.network(
    'https://cdn.syncfusion.com/content/PDFViewer/flutter- 
    succinctly.pdf',
    key: _pdfViewerKey,
  ),
);
}
}

我试过使用pdf_render软件包，它对我很有效，这个软件包也可以直接从url加载pdf文档。

PdfViewer.openFutureFile(
      // Accepting function that returns Future<String> of PDF file path
      () async => (await DefaultCacheManager().getSingleFile(
              'https://github.com/espresso3389/flutter_pdf_render/raw/master/example/assets/hello.pdf'))
          .path,
      viewerController: controller,
      onError: (err) => print(err),
      params: const PdfViewerParams(
        padding: 10,
        minScale: 1.0,
        // scrollDirection: Axis.horizontal,
      ),
    ))