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 header = file.peekBytes(4);
  return bytesToString(header) === "ttcf";
}
function isOpenTypeFile(file) {
  const header = file.peekBytes(4);
  return bytesToString(header) === "OTTO";
}
function isType1File(file) {
  const header = file.peekBytes(2);
  
  if (header[0] === 0x25 && header[1] === 0x21) {
    return true;
  }
  
  
  if (header[0] === 0x80 && header[1] === 0x01) {
    return true;
  }
  return false;
}
/**
 * Compared to other font formats, the header in CFF files is not constant
 * but contains version numbers. To reduce the possibility of misclassifying
 * font files as CFF, it's recommended to check for other font formats first.
 */
function isCFFFile(file) {