This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
try {
          newPdfManager = new LocalPdfManager(
            docId,
            pdfFile,
            source.password,
            evaluatorOptions,
            docBaseUrl
          );
          pdfManagerCapability.resolve(newPdfManager);
        } catch (ex) {
          pdfManagerCapability.reject(ex);
        }
        cachedChunks = [];
      };
      var readPromise = new Promise(function (resolve, reject) {
        var readChunk = function ({ value, done }) {
          try {
            ensureNotTerminated();
            if (done) {
              if (!newPdfManager) {
                flushChunks();
              }
              cancelXHRs = null;
              return;
            }
            loaded += arrayByteLength(value);
            if (!fullRequest.isStreamingSupported) {
              handler.send("DocProgress", {
                loaded,