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.
hPadding,
      vPadding
    );
    return (
      "/Tx BMC q BT " +
      defaultAppearance +
      ` 1 0 0 1 0 0 Tm ${renderedText}` +
      " ET Q EMC"
    );
  }
  async _getFontData(evaluator, task) {
    const operatorList = new OperatorList();
    const initialState = {
      fontSize: 0,
      font: null,
      fontName: null,
      clone() {
        return this;
      },
    };
    await evaluator.getOperatorList({
      stream: new StringStream(this.data.defaultAppearance),
      task,
      resources: this._fieldResources.mergedResources,
      operatorList,
      initialState,
    });
    return [initialState.font, initialState.fontName, initialState.fontSize];
  }
  _computeFontSize(font, fontName, fontSize, height) {