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)

} else {
            for (j = 0; j < n; j++) {
              stack.push(data[i++]);
            }
          }
        } else if ((op & 0xf8) === 0xb8) {
          
          n = op - 0xb8 + 1;
          if (inFDEF || inELSE) {
            i += n * 2;
          } else {
            for (j = 0; j < n; j++) {
              b = data[i++];
              stack.push((b << 8) | data[i++]);
            }
          }
        } else if (op === 0x2b && !tooComplexToFollowFunctions) {
          
          if (!inFDEF && !inELSE) {
            
            funcId = stack[stack.length - 1];
            if (isNaN(funcId)) {
              info("TT: CALL empty stack (or invalid entry).");
            } else {
              ttContext.functionsUsed[funcId] = true;
              if (funcId in ttContext.functionsStackDeltas) {
                const newStackLength =
                  stack.length + ttContext.functionsStackDeltas[funcId];
                if (newStackLength < 0) {
                  warn("TT: CALL invalid functions stack delta.");