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._setRequired(event.target, event.detail.required);
      },
      bgColor: event => {
        setColor("bgColor", "backgroundColor", event);
      },
      fillColor: event => {
        setColor("fillColor", "backgroundColor", event);
      },
      fgColor: event => {
        setColor("fgColor", "color", event);
      },
      textColor: event => {
        setColor("textColor", "color", event);
      },
      borderColor: event => {
        setColor("borderColor", "borderColor", event);
      },
      strokeColor: event => {
        setColor("strokeColor", "borderColor", event);
      },
      rotation: event => {
        const angle = event.detail.rotation;
        this.setRotation(angle);
        this.annotationStorage.setValue(this.data.id, {
          rotation: angle,
        });
      },
    });
  }
  _dispatchEventFromSandbox(actions, jsEvent) {