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.appearance = null;
    const appearanceStates = dict.get("AP");
    if (!isDict(appearanceStates)) {
      return;
    }
    
    const normalAppearanceState = appearanceStates.get("N");
    if (isStream(normalAppearanceState)) {
      this.appearance = normalAppearanceState;
      return;
    }
    if (!isDict(normalAppearanceState)) {
      return;
    }
    
    
    const as = dict.get("AS");
    if (!isName(as) || !normalAppearanceState.has(as.name)) {
      return;
    }
    this.appearance = normalAppearanceState.get(as.name);
  }
  loadResources(keys) {