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):

constructor(parameters) {
    const isRenderable =
      parameters.renderForms ||
      (!parameters.data.hasAppearance && !!parameters.data.fieldValue);
    super(parameters, { isRenderable });
  }
  setPropertyOnSiblings(base, key, value, keyInStorage) {
    const storage = this.annotationStorage;
    for (const element of this._getElementsByName(
      base.name,
       base.id
    )) {
      if (element.domElement) {
        element.domElement[key] = value;
      }
      storage.setValue(element.id, { [keyInStorage]: value });
    }
  }
  render() {
    const storage = this.annotationStorage;
    const id = this.data.id;
    this.container.classList.add("textWidgetAnnotation");
    let element = null;
    if (this.renderForms) {