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):

const { data, linkService } = this;
    const link = document.createElement("a");
    link.setAttribute("data-element-id", data.id);
    let isBound = false;
    if (data.url) {
      linkService.addLinkAttributes(link, data.url, data.newWindow);
      isBound = true;
    } else if (data.action) {
      this._bindNamedAction(link, data.action);
      isBound = true;
    } else if (data.attachment) {
      this._bindAttachment(link, data.attachment);
      isBound = true;
    } else if (data.setOCGState) {
      this.#bindSetOCGState(link, data.setOCGState);
      isBound = true;
    } else if (data.dest) {
      this._bindLink(link, data.dest);
      isBound = true;
    } else {
      if (
        data.actions &&
        (data.actions.Action ||
          data.actions["Mouse Up"] ||
          data.actions["Mouse Down"]) &&
        this.enableScripting &&
        this.hasJSActions