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.
constructor(params) {
    super(params);
    this.data.annotationType = AnnotationType.LINK;
    const quadPoints = getQuadPoints(params.dict, this.rectangle);
    if (quadPoints) {
      this.data.quadPoints = quadPoints;
    }
    Catalog.parseDestDictionary({
      destDict: params.dict,
      resultObj: this.data,
      docBaseUrl: params.pdfManager.docBaseUrl,
    });
  }
}
class PopupAnnotation extends Annotation {