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.
}
    
    const encodedString = font.encodeString(value).join("");
    if (this.data.comb) {
      return this._getCombAppearance(
        defaultAppearance,
        font,
        encodedString,
        totalWidth,
        hPadding,
        vPadding
      );
    }
    if (alignment === 0 || alignment > 2) {
      
      return (
        "/Tx BMC q BT " +
        defaultAppearance +
        ` 1 0 0 1 ${hPadding} ${vPadding} Tm (${escapeString(
          encodedString
        )}) Tj` +
        " ET Q EMC"
      );
    }
    const renderedText = this._renderText(
      encodedString,
      font,
      fontSize,
      totalWidth,
      alignment,