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 commonActions = this._commonActions;
    for (const name of Object.keys(jsEvent.detail)) {
      const action = actions[name] || commonActions[name];
      action?.(jsEvent);
    }
  }
  _setDefaultPropertiesFromJS(element) {
    if (!this.enableScripting) {
      return;
    }
    
    const storedData = this.annotationStorage.getRawValue(this.data.id);
    if (!storedData) {
      return;
    }
    const commonActions = this._commonActions;
    for (const [actionName, detail] of Object.entries(storedData)) {
      const action = commonActions[actionName];
      if (action) {
        const eventProxy = {
          detail: {
            [actionName]: detail,
          },
          target: element,
        };
        action(eventProxy);
        
        delete storedData[actionName];
      }
    }