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)

(baseEncoding.length || this.differences.length)
      ) {
        for (let i = 0; i < 256; ++i) {
          if (!forcePostTable && charCodeToGlyphId[i] !== undefined) {
            continue;
          }
          const glyphName = this.differences[i] || baseEncoding[i];
          if (!glyphName) {
            continue;
          }
          const glyphId = properties.glyphNames.indexOf(glyphName);
          if (glyphId > 0 && hasGlyph(glyphId)) {
            charCodeToGlyphId[i] = glyphId;
          }
        }
      }
    }
    if (charCodeToGlyphId.length === 0) {
      
      charCodeToGlyphId[0] = 0;
    }
    
    
    
    
    let glyphZeroId = numGlyphsOut - 1;
    if (!dupFirstEntry) {
      glyphZeroId = 0;
    }