Viewer:  https://mozilla.github.io/pdf.js/web/viewer.html
Chrome on Windows 10
When the attached PDF file is viewed, some of the fonts display as garbled text. 
[Arial, Courier, Times New Roman]
The file views correctly in Adobe Reader.
[fff.pdf](https://github.com/mozilla/pdf.js/files/4652174/fff.pdf)

if (properties.isInternalFont) {
    return;
  }
  if (builtInEncoding === properties.defaultEncoding) {
    return; 
  }
  if (properties.toUnicode instanceof IdentityToUnicodeMap) {
    return;
  }
  const toUnicode = [],
    glyphsUnicodeMap = getGlyphsUnicode();
  for (const charCode in builtInEncoding) {
    if (properties.hasIncludedToUnicodeMap) {
      if (properties.toUnicode.has(charCode)) {
        continue; 
      }
    } else {
      if (
        properties.hasEncoding &&
        properties.differences[charCode] !== undefined
      ) {
        continue; 
      }
    }
    const glyphName = builtInEncoding[charCode];
    const unicode = getUnicodeForGlyph(glyphName, glyphsUnicodeMap);
    if (unicode !== -1) {