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.
this.creationDate = isString(creationDate) ? creationDate : null;
  }
  _setDefaultAppearance({
    xref,
    extra,
    strokeColor,
    fillColor,
    blendMode,
    pointsCallback,
  }) {
    let minX = Number.MAX_VALUE;
    let minY = Number.MAX_VALUE;
    let maxX = Number.MIN_VALUE;
    let maxY = Number.MIN_VALUE;
    const buffer = ["q"];
    if (extra) {
      buffer.push(extra);
    }
    if (strokeColor) {
      buffer.push(`${strokeColor[0]} ${strokeColor[1]} ${strokeColor[2]} RG`);
    }
    if (fillColor) {
      buffer.push(`${fillColor[0]} ${fillColor[1]} ${fillColor[2]} rg`);
    }
    for (const points of this.data.quadPoints) {
      const [mX, MX, mY, MY] = pointsCallback(buffer, points);
      minX = Math.min(minX, mX);
      maxX = Math.max(maxX, MX);
      minY = Math.min(minY, mY);