
Attach (recommended) or Link to PDF file here:
[NAPEN16171380959.pdf](https://github.com/mozilla/pdf.js/files/6143802/NAPEN16171380959.pdf)

Configuration:
- Web browser and its version: Firefox 88 Nightly
- Operating system and its version: Windows 10
- PDF.js version:
- Is a browser extension: No

What went wrong? (add screenshot)
![](https://user-media-prod-cdn.itsre-sumo.mozilla.net/uploads/images/2021-03-15-10-58-27-ce2796.png)


var toFontChar = [],
      unicode;
    for (var i = 0, ii = encoding.length; i < ii; i++) {
      unicode = getUnicodeForGlyph(encoding[i], glyphsUnicodeMap);
      if (unicode !== -1) {
        toFontChar[i] = unicode;
      }
    }
    for (var charCode in differences) {
      unicode = getUnicodeForGlyph(differences[charCode], glyphsUnicodeMap);
      if (unicode !== -1) {
        toFontChar[+charCode] = unicode;
      }
    }
    return toFontChar;
  }
  /**
   * Rebuilds the char code to glyph ID map by moving all char codes to the
   * private use area. This is done to avoid issues with various problematic
   * unicode areas where either a glyph won't be drawn or is deformed by a
   * shaper.
   * @returns {Object} Two properties:
   * 'toFontChar' - maps original char codes(the value that will be read
   * from commands such as show text) to the char codes that will be used in the
   * font that we build
   * 'charCodeToGlyphId' - maps the new font char codes to glyph ids
   */
  function adjustMapping(charCodeToGlyphId, hasGlyph, newGlyphZeroId) {