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):

imageResourcesPath: params.imageResourcesPath || "",
      renderForms: params.renderForms !== false,
      svgFactory: new DOMSVGFactory(),
      annotationStorage: params.annotationStorage || new AnnotationStorage(),
      enableScripting: params.enableScripting === true,
      hasJSActions: params.hasJSActions,
      fieldObjects: params.fieldObjects,
      parent: this,
      elements: null,
    };
    for (const data of annotations) {
      if (data.noHTML) {
        continue;
      }
      const isPopupAnnotation = data.annotationType === AnnotationType.POPUP;
      if (!isPopupAnnotation) {
        const { width, height } = getRectDims(data.rect);
        if (width <= 0 || height <= 0) {
          continue; 
        }
      } else {
        const elements = popupToElements.get(data.id);
        if (!elements) {
          
          continue;
        }
        elementParams.elements = elements;
      }
      elementParams.data = data;
      const element = AnnotationElementFactory.create(elementParams);