CONSOLE MESSAGE: webviewerloaded: SecurityError: Blocked a frame with origin "webkit-pdfjs-viewer://pdfjs" from accessing a cross-origin frame. Protocols, domains, and ports must match.

This happens when the pdf viewer is loaded because it tries to dispatch a custom event to the parent document:

function webViewerLoad() {
  const config = getViewerConfiguration();
  const event = document.createEvent("CustomEvent");
  event.initCustomEvent("webviewerloaded", true, true, {
    source: window
  });

  try {
    parent.document.dispatchEvent(event);
  } catch (ex) {
    console.error(`webviewerloaded: ${ex}`);
    document.dispatchEvent(event);
  }

  _app.PDFViewerApplication.run(config);
}

I have no idea why that's done, but I guess it's harmless and doesn't affect any functionality.

CONSOLE MESSAGE: Feature policy 'Fullscreen' check failed for iframe with origin 'webkit-pdfjs-viewer://pdfjs' and allow attribute ''.

This happens when the viewer checks is fullscreen is supported to enable the presentation mode.