private void RadPdfViewer1_MouseUp(object sender, MouseEventArgs e)
{
    foreach (RadFixedPageElement visualPage in this.radPdfViewer1.PdfViewerElement.ViewElement.Children)
    {
        foreach (RadElement editorElement in visualPage.Children)
        {
            if (editorElement is RadDropDownListElement dropDownListElement)
            {
                var collection = (dropDownListElement.DataSource as IEnumerable<ChoiceOption>);
                if (collection.Where(x => x.UserInterfaceValue != null).Count() == collection.Count())
                {
                    dropDownListElement.DisplayMember = "UserInterfaceValue";
                }              
            }

            if (editorElement is RadListElement listElement)
            {
                var collection=  (listElement.DataSource as IEnumerable<ChoiceOption>);
                if (collection.Where(x=>x.UserInterfaceValue !=null).Count() == collection.Count())
                {
                    listElement.DisplayMember = "UserInterfaceValue";
                }
            }                  
        }
    }
}