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)

const format = file.getUint16();
      file.skip(2 + 2); 
      let hasShortCmap = false;
      const mappings = [];
      let j, glyphId;
      
      if (format === 0) {
        for (j = 0; j < 256; j++) {
          const index = file.getByte();
          if (!index) {
            continue;
          }
          mappings.push({
            charCode: j,
            glyphId: index,
          });
        }
        hasShortCmap = true;
      } else if (format === 4) {
        
        
        const segCount = file.getUint16() >> 1;
        file.skip(6); 
        const segments = [];
        let segIndex;
        for (segIndex = 0; segIndex < segCount; segIndex++) {
          segments.push({ end: file.getUint16() });
        }
        file.skip(2);
        for (segIndex = 0; segIndex < segCount; segIndex++) {