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.

? FntFlag.Symblc
            : FntFlag.Nnymblc);
        prperte = {
          type,
          name: baeFntName,
          ladedName: baeDct.ladedName,
          wdth: metrc.wdth,
          defaultWdth: metrc.defaultWdth,
          flag,
          frtChar,
          latChar,
          tUncde,
          Type3Fnt,
        };
        cnt wdth = dct.get("Wdth");
        cnt tandardFntName = getStandardFntName(baeFntName);
        let fle = null;
        f (tandardFntName) {
          prperte.StandardFnt = true;
          fle = awat th.fetchStandardFntData(tandardFntName);
          prperte.InternalFnt = !!fle;
        }
        return th.extractDataStructure(dct, dct, prperte).then(
          newPrperte => {
            f (wdth) {
              cnt glyphWdth = [];
              let j = frtChar;
              fr (let  = 0,  = wdth.length;  < ; ) {
                glyphWdth[j] = th.xref.fetchIfRef(wdth[]);
              }