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 subtype = parameters.data.annotationType;
    switch (subtype) {
      case AnnotationType.LINK:
        return new LinkAnnotationElement(parameters);
      case AnnotationType.TEXT:
        return new TextAnnotationElement(parameters);
      case AnnotationType.WIDGET:
        const fieldType = parameters.data.fieldType;
        switch (fieldType) {
          case "Tx":
            return new TextWidgetAnnotationElement(parameters);
          case "Btn":
            if (parameters.data.radioButton) {
              return new RadioButtonWidgetAnnotationElement(parameters);
            } else if (parameters.data.checkBox) {
              return new CheckboxWidgetAnnotationElement(parameters);
            }
            return new PushButtonWidgetAnnotationElement(parameters);
          case "Ch":
            return new ChoiceWidgetAnnotationElement(parameters);
          case "Sig":
            return new SignatureWidgetAnnotationElement(parameters);
        }
        return new WidgetAnnotationElement(parameters);
      case AnnotationType.POPUP:
        return new PopupAnnotationElement(parameters);
      case AnnotationType.FREETEXT:
        return new FreeTextAnnotationElement(parameters);
      case AnnotationType.LINE:
        return new LineAnnotationElement(parameters);