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):

if (this.data.hasOwnCanvas) {
      if (element.previousSibling?.nodeName === "CANVAS") {
        element.previousSibling.hidden = true;
      }
      element.hidden = false;
    }
  }
  _getKeyModifier(event) {
    const { isWin, isMac } = FeatureTest.platform;
    return (isWin && event.ctrlKey) || (isMac && event.metaKey);
  }
  _setEventListener(element, elementData, baseName, eventName, valueGetter) {
    if (baseName.includes("mouse")) {
      
      element.addEventListener(baseName, event => {
        this.linkService.eventBus?.dispatch("dispatcheventinsandbox", {
          source: this,
          detail: {
            id: this.data.id,
            name: eventName,
            value: valueGetter(event),
            shift: event.shiftKey,
            modifier: this._getKeyModifier(event),
          },
        });