This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
source.password,
            evaluatorOptions,
            docBaseUrl
          );
          pdfManagerCapability.resolve(newPdfManager);
        } catch (ex) {
          pdfManagerCapability.reject(ex);
        }
        return pdfManagerCapability.promise;
      }
      var pdfStream,
        cachedChunks = [];
      try {
        pdfStream = new PDFWorkerStream(handler);
      } catch (ex) {
        pdfManagerCapability.reject(ex);
        return pdfManagerCapability.promise;
      }
      var fullRequest = pdfStream.getFullReader();
      fullRequest.headersReady
        .then(function () {
          if (!fullRequest.isRangeSupported) {
            return;
          }
          
          var disableAutoFetch =
            source.disableAutoFetch || fullRequest.isStreamingSupported;
          newPdfManager = new NetworkPdfManager(
            docId,
            pdfStream,