https://github.com/mozilla/pdf.js/issues/6397#issuecomment-164954332 Would have been a lot easier to find had there been an assertion checking that string16 didn't go out of bounds of the 16bit number.

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) {