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):

element.type = "radio";
    element.name = data.fieldName;
    if (value) {
      element.setAttribute("checked", true);
    }
    element.tabIndex = DEFAULT_TAB_INDEX;
    element.addEventListener("change", event => {
      const { name, checked } = event.target;
      for (const radio of this._getElementsByName(name,  id)) {
        storage.setValue(radio.id, { value: false });
      }
      storage.setValue(id, { value: checked });
    });
    element.addEventListener("resetform", event => {
      const defaultValue = data.defaultFieldValue;
      event.target.checked =
        defaultValue !== null &&
        defaultValue !== undefined &&
        defaultValue === data.buttonValue;
    });
    if (this.enableScripting && this.hasJSActions) {
      const pdfButtonValue = data.buttonValue;
      element.addEventListener("updatefromsandbox", jsEvent => {
        const actions = {
          value: event => {
            const checked = pdfButtonValue === event.detail.value;
            for (const radio of this._getElementsByName(event.target.name)) {
              const curChecked = checked && radio.id === id;
              if (radio.domElement) {
                radio.domElement.checked = curChecked;