Can I add a link to my ORCID Id in the statement of purpose?
Your ORCID would be better off placed on your CV, either next to or below your name. You can certainly cite your published paper in your statement of purpose, if it is relevant to the work you want to pursue in your PhD. You should also list your publications on your CV. It might be worth looking at the websites of a few professors in your field, to find examples of how they structure and format their CVs.