This item is declined because there are many PDF annotation types and we are going to create separate items for each type. You may follow some of the existing annotation feedback items listed below or create a new one which the Telerik team is going to approve. Here follows the list of the existing feedback items:
https://feedback.telerik.com/Project/143/Feedback/Details/167439-pdfviewer-support-for-annotations-of-type-stamp
https://feedback.telerik.com/Project/143/Feedback/Details/203379-pdfviewer-support-for-annotations-of-type-popup
https://feedback.telerik.com/Project/143/Feedback/Details/199351-pdfviewer-support-for-freetext-annotation-type
https://feedback.telerik.com/Project/143/Feedback/Details/149974-pdfviewer-highlight-annotation