public void UpdateThumbnailEx()
        {
            //ExStart
            //ExFor:Document.UpdateThumbnail()
            //ExFor:Document.UpdateThumbnail(ThumbnailGeneratingOptions)
            //ExSummary:Shows how to update a document's thumbnail.
            Document doc = new Document();

            // Update document's thumbnail the default way. 
            doc.UpdateThumbnail();

            // Review/change thumbnail options and then update document's thumbnail.
            ThumbnailGeneratingOptions tgo = new ThumbnailGeneratingOptions();

            Console.WriteLine("Thumbnail size: {0}", tgo.ThumbnailSize);
            tgo.GenerateFromFirstPage = true;

            doc.UpdateThumbnail(tgo);
            //ExEnd
        }