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):

this.downloadManager?.openOrDownloadData(
      this.container,
      this.content,
      this.filename
    );
  }
}
/**
 * @typedef {Object} AnnotationLayerParameters
 * @property {PageViewport} viewport
 * @property {HTMLDivElement} div
 * @property {Array} annotations
 * @property {PDFPageProxy} page
 * @property {IPDFLinkService} linkService
 * @property {IDownloadManager} downloadManager
 * @property {AnnotationStorage} [annotationStorage]
 * @property {string} [imageResourcesPath] - Path for image resources, mainly
 *   for annotation icons. Include trailing slash.
 * @property {boolean} renderForms
 * @property {boolean} [enableScripting] - Enable embedded script execution.
 * @property {boolean} [hasJSActions] - Some fields have JS actions.
 *   The default value is `false`.
 * @property {Object<string, Array<Object>> | null} [fieldObjects]
 * @property {Map<string, HTMLCanvasElement>} [annotationCanvasMap]
 * @property {TextAccessibilityManager} [accessibilityManager]
 */
/**
 * Manage the layer containing all the annotations.
 */
class AnnotationLayer {