Exception handling?

In my below foobar first attempt to try exception handling I don't understand
the following aspects: (my code at bottom after these framework pastes)

1. I must not be doing something correct because even though both
my CATCH and AND_CATCH call stuff on return that appears to be
deleting the exception and taking care of various cleanup.

// abbreviated Step thru pastes
//---------------------------------------
void AFXAPI AfxTryCleanup( )
{
   ......
   .....
  // delete current exception
  ASSERT(pLinkTop != NULL);
  if (pLinkTop->m_pException != NULL)
    pLinkTop->m_pException->Delete( );
 .....
 .....
}
// and later
CString::~CString()
 // free any attached data
{
  ....etc etc
}
//--------------------------------------
* * when the exception returns back to document caller I don't see this
* * getting executed,

  if (!pDocument->OnNewDocument())
  {
    // user has been alerted to what failed in OnNewDocument
    TRACE0("CDocument::OnNewDocument returned FALSE.\n");
    if (bCreated)
      pFrame->DestroyWindow(); // will destroy document
    return NULL;
  }
  .....
  .......
// Instead I see this down the road,
 
CDocument* CWinApp::OpenDocumentFile(LPCTSTR lpszFileName)
{
 ASSERT(m_pDocManager != NULL);
    //* *And lpszPathName still = TheFileNameItriedToOpen ? * *
 return m_pDocManager->OpenDocumentFile(lpszFileName);
}
//* *
So if I save my document after code turns app back over to me I overwrite
the file that I could not open ? So there must be more " I " have to do, or something
different if I have it all wrong out of the shute.

2. Also from the docs I have read I got the impression that by putting THROW_LAST( );
    at the end of my CATCH( CUserException, e ) that it would forward the exception
    to my AND_CATCH( CException, e ) but experimentation shows that does not
    happen, so I missed something there. But anyhow both exceptions seem to pass
    to clean up code on return so question 2 is only a curiousity. Question 1 is my
    main concern.

=== foobar attempt below ====

void CFileHandlingDoc::Serialize(CArchive& ar)
{
 if (ar.IsStoring())
   {
      ar << FileID; // DWORD
     ar << VerData.Ver << VerData.CpyRt << VerData.Corp;
     ar.SerializeClass(RUNTIME_CLASS(CMapStringToString));
     ExpMap1.Serialize(ar);
   }
 else
   {
     CString E;
     TCHAR szErrMsg[255];
     TRY
      {
        ar >> FileID;
        if (FileID != 0x1234ABCD)
          { // FileID mismatch
            AfxThrowUserException( );
          }
        ar >> VerData.Ver >> VerData.CpyRt >> VerData.Corp;
        ar.SerializeClass(RUNTIME_CLASS(CMapStringToString)); // WriteClass CmStS's data
        ExpMap1.Serialize(ar); // CMapStringToString's keys and values
         
      }
     CATCH( CUserException, e )
      {
        E = _T("BAD FileID, RB from inside CATCH\n");
        AfxMessageBox( E );
        return;
      }
     AND_CATCH( CException, e )
      {
        // For other exception types, notify user here.
        e->GetErrorMessage(szErrMsg, 255);
        E = _T("RB from inside AND_CATCH\n");
        E += szErrMsg;
        AfxMessageBox( E );
        return;
      }
     END_CATCH
        // No exception thrown.
   }
}