In file https://github.com/mozilla/pdf.js/files/5249872/product1.pdf, the fifth text widget has a default appearance using font F1 and this one is neither in DR nor in AcroForm but in AP::N::Resources.
if (
      typeof PDFJSDev === "undefined" ||
      PDFJSDev.test("!PRODUCTION || TESTING")
    ) {
      assert(
        this._fontName !== undefined,
        "Expected `_getAppearance()` to have been called."
      );
    }
    const { localResources, acroFormResources } = this._fieldResources;
    if (!this._fontName) {
      return localResources || Dict.empty;
    }
    if (localResources instanceof Dict) {
      const localFont = localResources.get("Font");
      if (localFont instanceof Dict && localFont.has(this._fontName)) {
        return localResources;