Open a local PDF in an UWP application (HoloLens)

I want to open a PDF file that is stored in the Application.persistentDataPath. This works inside the Unity Editor, but on the HoloLens I see this:

public void LoadPdf(string file)
{
  var _webView = GetComponent< WebView >();
   _webView.GetWebViewWhenReady((IWebView webView) =>
  {
      webView.Load(new Uri(FileToUrl(file));
  });
}

 private string FileToUrl(string pdfFile)
            => ("file://" + Application.persistentDataPath + "/" + pdfFile).Replace(" ", "%20"); 

Is there a different way to format the uri to a locally stored PDF or can I somehow change the restrictions of the WebView, to display PDFs from the local file system?

AB#46433231