pdf_view.dart

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("Abrir pdf"),
        ),
        body: Center(
          child: Builder(
            builder: (context) => Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    RaisedButton(
                      color: Colors.amber,
                      child: Text("Abrir desde la URL"),
                      onPressed: () {
                        if (urlPDFPath != null) {
                          Navigator.push(
                              context,
                              MaterialPageRoute(
                                  builder: (context) =>
                                      PdfViewPage(path: urlPDFPath)));
                        }
                      },
                    ),
                    SizedBox(
                      height: 20,
                    ),
                    RaisedButton(
                      color: Colors.cyan,
                      child: Text("Abrir desde la carpeta"),
                      onPressed: () {
                        if (assetPDFPath != null) {
                          Navigator.push(
                              context,
                              MaterialPageRoute(
                                  builder: (context) =>
                                      PdfViewPage(path: assetPDFPath)));
                        }
                      },
                    )
                  ],
                ),
          ),
        ),
      ),
    );
  }