TOPIC:

public Task<ICorePdfAnnotation> AddHighlight(ICorePdfSel selection, string color)
		{
			if (!InitObjs()) return Task.FromResult((ICorePdfAnnotation)null);

			var status = NativePage?.AddAnnotMarkup(selection.StartIndex, selection.EndIndex, 0) == true;
			ICorePdfAnnotation result = null;

			if (status)
			{
				var annotation = NativePage?.GetAnnot(NativePage.AnnotCount - 1);
				var colorObj = Color.ParseColor(color);

				annotation.SetFillColor(colorObj.ToArgb());
				annotation.SetName("Test");

				result = new AndroidPdfAnnotationWrapper(annotation);
			}

			return Task.FromResult(result);
		}

public class AndroidPdfAnnotationWrapper : ICorePdfAnnotation
	{
		private Page.Annotation annotation;

		public AndroidPdfAnnotationWrapper(Page.Annotation annotation)
		{
			this.annotation = annotation;
		}

		public bool Remove()
		{
			var status = annotation.RemoveFromPage();
			return status;
		}
	}

Document document = new Document();
            if (document.Open(path, "") == 0)
            {
                bool result = false;
                Page page = document.GetPage(0);
                page.ObjsStart();
                if (page.AddAnnotMarkup(170, 616, 0))
                {
                    Page.Annotation annot = page.GetAnnot(page.AnnotCount - 1); 
                    if (annot != null)
                    {
                        result = annot.RemoveFromPage();
                    }
                }
            }