/// <summary>
 /// Removes the page at <paramref name="index"/>.
 /// </summary>
 public void RemoveAt(int index)
 {
     if (index < _pages.Count)
     {
         ((IDisposable)_pages[index])?.Dispose();
         _pages.RemoveAt(index);
         for (int i = index; i < _pages.Count; i++)
         {
             if (_pages[i] != null)
             {
                 _pages[i].Index = i;
             }
         }
     }
     PDFium.FPDFPage_Delete(_doc.Handle, index);
 }