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):

#onPresentationModeChanged = null;
  /**
   * @param {AnnotationLayerBuilderOptions} options
   */
  constructor({
    pageDiv,
    pdfPage,
    linkService,
    downloadManager,
    annotationStorage = null,
    imageResourcesPath = "",
    renderForms = true,
    l10n = NullL10n,
    enableScripting = false,
    hasJSActionsPromise = null,
    fieldObjectsPromise = null,
    annotationCanvasMap = null,
    accessibilityManager = null,
  }) {
    this.pageDiv = pageDiv;
    this.pdfPage = pdfPage;
    this.linkService = linkService;
    this.downloadManager = downloadManager;
    this.imageResourcesPath = imageResourcesPath;
    this.renderForms = renderForms;
    this.l10n = l10n;
    this.annotationStorage = annotationStorage;