Reading from the source code:

https://github.com/mozilla/pdf.js/blob/57d196e3497e77c81c19f852715ce79d9fb91492/src/display/annotation_layer.js#L2846

it appears to me it was not an intention to mark downloadManager as a required parameter in AnnotationLayerParameters:

https://github.com/mozilla/pdf.js/blob/57d196e3497e77c81c19f852715ce79d9fb91492/src/display/annotation_layer.js#L63

and AnnotationLayerBuilderOptions:

https://github.com/mozilla/pdf.js/blob/57d196e3497e77c81c19f852715ce79d9fb91492/web/annotation_layer_builder.js#L40

and it should be optional, similarly to accessibilityManager for example:

https://github.com/mozilla/pdf.js/blob/57d196e3497e77c81c19f852715ce79d9fb91492/web/text_layer_builder.js#L30

**Configuration:**
- PDF.js version: 2.11.174
- Is a browser extension: no

**What is the expected behavior? (add screenshot)**

`downloadManager` to be optional

**What went wrong? (add screenshot)**

`downloadManager` marked as required

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

*     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import { AnnotationLayer } from "pdfjs-lib";
import { NullL10n } from "./l10n_utils.js";
import { PresentationModeState } from "./ui_utils.js";
/**
 * @typedef {Object} AnnotationLayerBuilderOptions
 * @property {HTMLDivElement} pageDiv
 * @property {PDFPageProxy} pdfPage
 * @property {AnnotationStorage} [annotationStorage]
 * @property {string} [imageResourcesPath] - Path for image resources, mainly
 *   for annotation icons. Include trailing slash.
 * @property {boolean} renderForms
 * @property {IPDFLinkService} linkService
 * @property {IDownloadManager} downloadManager
 * @property {IL10n} l10n - Localization service.
 * @property {boolean} [enableScripting]
 * @property {Promise<boolean>} [hasJSActionsPromise]
 * @property {Promise<Object<string, Array<Object>> | null>}
 *   [fieldObjectsPromise]
 * @property {Map<string, HTMLCanvasElement>} [annotationCanvasMap]
 * @property {TextAccessibilityManager} [accessibilityManager]
 */
class AnnotationLayerBuilder {