self.load(QUrl.fromUserInput(f'{PDFJS}?file={PDF}'))

import sys
import os
from PyQt5.QtWidgets import QApplication
from PyQt5.QtCore import QUrl
from PyQt5.QtWebEngineWidgets import QWebEngineView
import requests

url = "http://www.tabularium.be/bailly/0001.pdf"

content = requests.get(url).content

with open("/tmp/test.pdf", 'wb') as f:
    f.write(content)

PDFJS = f"file://{os.path.abspath('./web/viewer.html')}"
print(PDFJS)
PDF = "file:///tmp/test.pdf"
print("loading PDF:", PDF)

class Window(QWebEngineView):
    def __init__(self):
        super(Window, self).__init__()
        self.load(QUrl.fromUserInput(f'{PDFJS}?file={PDF}'))
        self.setZoomFactor(0.25)

if __name__ == '__main__':

    app = QApplication(sys.argv)
    window = Window()
    window.showMaximized()
    sys.exit(app.exec_())