Save annotations to a separate file

Can I save the annotations to a different file and not into the PDF itself?

I want to share the annotations between different platforms, ie, if a user create an annotation in IOs he can read see the same annotation in Android obviously I'll keep sync the annotation file between the platforms.

Thanks,

We started evaluating that features some month ago but freezed the development process because annotations could be really complex structures.
When we will provide full API to support export import for annotations we should support all the annotations, also from other editor/tools/generators.