richEbitBox.Document.Selection.SetRange(0, richEbitBox.Document.Selection.EndPosition);

            var id = sender as ComboBox;
            switch (id.Tag) {

                case "1":
                    //Todo implement new font name
                    string fontName = id.SelectedItem.ToString();
                    richEbitBox.Document.Selection.CharacterFormat.Name = fontName;
                    break;
                case "2":
                    var size = (float)id.SelectedItem;
                    //set size to the Selection
                    richEbitBox.Document.Selection.CharacterFormat.Size = size;
                    break;
                default:
                    break;
            }