Hi Enrico,
Thank you for your update.
PDF Viewer for WinRT platform internally uses Microsoft rendering engine to generate images of the pages of the PDF document and this support displaying all the elements that are supported by Microsoft rendering engine. At present, Microsoft rendering engine supports viewing PDF annotations in the graphics level. However, it will not be interactive as in adobe.
Please, let us know if you need any further assistance.
Thanks,
Uthistran S.