home page ts file after calling pdf download and view service

home.page.ts

import { File } from "@ionic-native/file/ngx";
import {
  FileTransfer,
  FileTransferObject
} from "@ionic-native/file-transfer/ngx";
import { FileOpener } from "@ionic-native/file-opener/ngx";
import { Injectable } from "@angular/core";

@Injectable({
  providedIn: "root"
})
export class PdfViewerService {
  fileTransfer: FileTransferObject;
  constructor(
    private fileOpener: FileOpener,
    private transfer: FileTransfer,
    private file: File
  ) {}

  download(url: string, title: string) {
    this.fileTransfer = this.transfer.create();
    this.fileTransfer
      .download(url, this.file.dataDirectory + title + ".pdf")
      .then(entry => {
        console.log("download complete: " + entry.toURL());
        this.fileOpener
          .open(entry.toURL(), "application/pdf")
          .then(() => console.log("File is opened"))
          .catch(e => console.log("Error opening file", e));
      });
  }
}

This is wrong. According of your tutorial https://ovpv.me/open-pdf-ionic-4/ this is not the PdfViewerService, else home.page.ts:
https://github.com/ovpv/pdfviewer-ionic-4/blob/master/src/app/home/home.page.ts