RGen_CreateBookmarks.cs

private void CreateBookmarks()
{
    PdfContentByte content = _writer.DirectContent;
    PdfOutline outline = content.RootOutline;

    foreach (var bookmark in Bookmarks)
    {
        if (bookmark.IsReleaseHeader)
            outline = CreatePdfOutline(content.RootOutline, bookmark);
        else
            CreatePdfOutline(outline, bookmark);
    }
}

private PdfOutline CreatePdfOutline(PdfOutline parent, Bookmark bookmark)
{
    return new PdfOutline(parent, PdfAction.GotoLocalPage(bookmark.PageNumber, new PdfDestination(bookmark.PageNumber), _writer), bookmark.Title);
}