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):

}
              storage.setValue(radio.id, { value: curChecked });
            }
          },
        };
        this._dispatchEventFromSandbox(actions, jsEvent);
      });
      this._setEventListeners(
        element,
        null,
        [
          ["change", "Validate"],
          ["change", "Action"],
          ["focus", "Focus"],
          ["blur", "Blur"],
          ["mousedown", "Mouse Down"],
          ["mouseenter", "Mouse Enter"],
          ["mouseleave", "Mouse Exit"],
          ["mouseup", "Mouse Up"],
        ],
        event => event.target.checked
      );
    }
    this._setBackgroundColor(element);
    this._setDefaultPropertiesFromJS(element);
    this.container.append(element);
    return this.container;
  }
}
class PushButtonWidgetAnnotationElement extends LinkAnnotationElement {