используйте
SPLimitedWebPartManager wpManager = page.GetLimitedWebPartManager(System.Web.UI.WebControls.WebParts.PersonalizationScope.Shared);
, затем по окончании наберите page.Update()
как то так
SPFile page = web.GetFile(string.Format("Pages/{0}", this.FileName.Replace("html", "aspx")));
SPLimitedWebPartManager wpManager = page.GetLimitedWebPartManager(System.Web.UI.WebControls.WebParts.PersonalizationScope.Shared);
SummaryLinkWebPart webpart = new SummaryLinkWebPart();
if (!string.IsNullOrEmpty(RelatedTopic1))
webpart.SummaryLinkValue.SummaryLinks.Add(GetSummaryLink(web, pages, RelatedTopic1));
if (!string.IsNullOrEmpty(RelatedTopic2))
webpart.SummaryLinkValue.SummaryLinks.Add(GetSummaryLink(web, pages, RelatedTopic2));
if (!string.IsNullOrEmpty(RelatedTopic3))
webpart.SummaryLinkValue.SummaryLinks.Add(GetSummaryLink(web, pages, RelatedTopic3));
if (!string.IsNullOrEmpty(RelatedTopic4))
webpart.SummaryLinkValue.SummaryLinks.Add(GetSummaryLink(web, pages, RelatedTopic4));
if (webpart.SummaryLinkValue.SummaryLinks.Count > 0)
{
wpManager.AddWebPart(webpart, "BottomPanel", 0);
page.Update();
}