You could check this article
from our documentation, which explains how to add a Bookmark to a RadDocument and here
is demonstrated how you could create a Hyperlink to this Bookmark.
However, if these resources are not helpful in the exact scenario, we will need some more information about the case. Are you importing a document containing bookmarks or it is created from scratch with RadRichTextBox? Could you verify that there is at least one bookmark in the document? The InsertHyperlinkDialog should show all the bookmarks, which are already inserted in the document.
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