/// <summary>
/// Add alternate content fallback
/// </summary>
/// <param name="alternateContentFallback"></param>
/// <returns></returns>
private string AddAlternateContentFallback(AlternateContentFallback alternateContentFallback)
{
foreach (OpenXmlElement element in alternateContentFallback.Elements())
if (element is Picture)
return AddPicture((Picture)element);
return "";
}