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.
maxY = Math.max(maxY, MY);
    }
    buffer.push("Q");
    const formDict = new Dict(xref);
    const appearanceStreamDict = new Dict(xref);
    appearanceStreamDict.set("Subtype", Name.get("Form"));
    const appearanceStream = new StringStream(buffer.join(" "));
    appearanceStream.dict = appearanceStreamDict;
    formDict.set("Fm0", appearanceStream);
    const gsDict = new Dict(xref);
    if (blendMode) {
      gsDict.set("BM", Name.get(blendMode));
    }
    const stateDict = new Dict(xref);
    stateDict.set("GS0", gsDict);
    const resources = new Dict(xref);
    resources.set("ExtGState", stateDict);
    resources.set("XObject", formDict);
    const appearanceDict = new Dict(xref);
    appearanceDict.set("Resources", resources);
    const bbox = (this.data.rect = [minX, minY, maxX, maxY]);
    appearanceDict.set("BBox", bbox);
    this.appearance = new StringStream("/GS0 gs /Fm0 Do");
    this.appearance.dict = appearanceDict;
    
    
    this._streams.push(this.appearance, appearanceStream);
  }
}
class WidgetAnnotation extends Annotation {