Ionic Object(...) не является функцией в DocumentViewer.viewDocument :

Я пытаюсь загрузить PDF-файл из папки с ресурсами в ionic или загрузить его. Я смотрел несколько руководств, но все они дают мне одну и ту же ошибку.

Ионный:

• ionic (Ionic CLI): 4.1.2 (C:\Users\hanna\node_modules\ionic)
• Ionic Framework: ионно-угловой 3.9.3
• @ionic/приложения-скрипты: 3.2.1

Кордова:

• кордова (CLI Cordova): 8.1.2 ([email protected])
• Платформы Cordova: Android 6.4.0, браузер 5.0.4.
• Плагины Cordova: Cordova-plugin-ionic-keyboard 2.1.3, cordova-plugin-ionic-webview 3.1.2 (и 7 других плагинов)

Система:

• NodeJS: v9.4.0 (C:\Program Files\nodejs\node.exe)
• нпм: 5.6.0
• ОС : Виндовс 10

Код :

import { Component } from '@angular/core';
import { DocumentViewer, DocumentViewerOptions } from '@ionic- 
native/document-viewer/ngx';
import { FileOpener } from '@ionic-native/file-opener/ngx';
import { FileTransfer } from '@ionic-native/file-transfer/ngx';
import { File } from '@ionic-native/File/ngx';
import { NavController, Platform } from 'ionic-angular';

@Component({
  selector: 'page-home',
templateUrl: 'home.html'
})
export class HomePage {
 constructor(
public navCtrl: NavController,
private file: File,
private ft: FileTransfer,
private document: DocumentViewer,
public platform: Platform
) {}
openLocalPdf() {
// let filePath = this.file.applicationDirectory + 'www/assets';

    // if (this.platform.is('android') || this.platform.is('browser')) {
//   let fakeName = Date.now();
//   this.file.copyFile(filePath, 'Typescript_Jumpstart_Book_Udemy.pdf', this.file.dataDirectory, `${fakeName}.pdf`).then(result => {
//     this.fileOpener.open(result.nativeURL, 'application/pdf')
//       .then(() => console.info('File is opened'))
//       .catch(e => console.info('Error opening file', e));
//   })
// } else {
//   // Use Document viewer for iOS for a better UI
//   const options: DocumentViewerOptions = {
//     title: 'My PDF'
//   }
//   this.document.viewDocument(`${filePath}/5-tools.pdf`, 'application/pdf', options);
// }
console.info('Documents Pressed.....');

    const options: DocumentViewerOptions = {
  title: "My PDF"
}
this.document.viewDocument('assets/Typescript_Jumpstart_Book_Udemy.pdf', 'application/pdf', options)
console.info('Documents Pressed..... afterrr');

  }
  downloadAndOpenPdf() {
let path = null;
if (this.platform.is('ios')) {
  path = this.file.documentsDirectory;
} else {
  path = this.file.dataDirectory;
}

    const transfer = this.ft.create();
transfer.download('https://devdactic.com/html/5-simple-hacks-LBT.pdf', path + 'MyFile.pdf').then(entry => {
  let url = entry.toURL();

      this.document.viewDocument(url, 'application/pdf', {});
  // this.fileOpener.open(url, 'application/pdf')
  // .then(() => console.info('File is opened'))
  // .catch(e => console.info('Error opening file', e));
 });
  }
}

Ошибка:

ERROR TypeError: Object(...) is not a function
at DocumentViewer.viewDocument (index.js:29)
at HomePage.webpackJsonp.193.HomePage.openLocalPdf (home.ts:43)
at Object.eval [as handleEvent] (HomePage.html:10)
at handleEvent (core.js:13589)
at callWithDebugContext (core.js:15098)
at Object.debugHandleEvent [as handleEvent] (core.js:14685)
at dispatchEvent (core.js:10004)
at core.js:10629
at HTMLButtonElement.<anonymous> (platform-browser.js:2628)
at t.invokeTask (polyfills.js:3)