To get a list of the annotation in a document, you need to do a simple loop like the following:
for (int i = 0; i < m_doc.GetPageCount(); i++) {
Page page = m_doc.GetPage(i);
page.ObjsStart();
for (int j = 0; j < page.GetAnnotCount(); j++) {
Annotation annot = page.GetAnnot(j);
//add it to your list
}
page.Close();
}