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.data.defaultAppearance = "/Helvetica 0 Tf 0 g";
    }
    const fontInfo = await this._getFontData(evaluator, task);
    const [font, fontName] = fontInfo;
    const fontSize = this._computeFontSize(...fontInfo, totalHeight);
    this._fontName = fontName;
    let descent = font.descent;
    if (isNaN(descent)) {
      descent = 0;
    }
    const vPadding = defaultPadding + Math.abs(descent) * fontSize;
    const defaultAppearance = this.data.defaultAppearance;
    const alignment = this.data.textAlignment;
    if (this.data.multiLine) {
      return this._getMultilineAppearance(
        defaultAppearance,
        value,
        font,
        fontSize,
        totalWidth,
        totalHeight,
        alignment,
        hPadding,
        vPadding
      );