public PdfDestination this[int index]
 {
     get
     {
         if (index < 0 || index >= Count)
         {
             throw new ArgumentOutOfRangeException(nameof(index));
         }
         (var handle, var name) = PDFium.FPDF_GetNamedDest(_doc.Handle, index);
         return(handle.IsNull ? null : new PdfDestination(_doc, handle, name));
     }
 }