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.
parentItem = parentItem.get("IRT");
    }
    if (!parentItem.has("M")) {
      this.data.modificationDate = null;
    } else {
      this.setModificationDate(parentItem.get("M"));
      this.data.modificationDate = this.modificationDate;
    }
    if (!parentItem.has("C")) {
      
      this.data.color = null;
    } else {
      this.setColor(parentItem.getArray("C"));
      this.data.color = this.color;
    }
    
    
    
    if (!this.viewable) {
      const parentFlags = parentItem.get("F");
      if (this._isViewable(parentFlags)) {
        this.setFlags(parentFlags);
      }
    }
    this.data.title = stringToPDFString(parentItem.get("T") || "");
    this.data.contents = stringToPDFString(parentItem.get("Contents") || "");
  }
}
class FreeTextAnnotation extends MarkupAnnotation {