The MFC CEdit class provides no simple way to prevent user from copying the contents of the corresponding Edit Control or pasting text into it or getting a context menu. Using subclassing and handling the WM_COPY, WM_PASTE, WM_CONTEXTMENU these operations can be disabled in a very simple way.

The code sample is very short and self explanatory. Most of the code is AppWizard generated. CPDEdit.* are the 2 main files of interest.

CPDEdit.h

-----------
class CPDEdit: public CEdit
{ 
public:
DECLARE_MESSAGE_MAP()
afx_msg LRESULT OnCopy(WPARAM, LPARAM);
afx_msg LRESULT OnPaste(WPARAM, LPARAM);
afx_msg LRESULT OnContextMenu(WPARAM, LPARAM);
}; 
CPDEdit.cpp
-----------
BEGIN_MESSAGE_MAP(CPDEdit, CEdit)
ON_MESSAGE(WM_COPY, OnCopy)
ON_MESSAGE(WM_PASTE, OnPaste)
ON_MESSAGE(WM_CONTEXTMENU, OnContextMenu)
END_MESSAGE_MAP()
LRESULT CPDEdit::OnCopy(WPARAM, LPARAM) {
return 0;
}
LRESULT CPDEdit::OnPaste(WPARAM, LPARAM) {
return 0;
}
LRESULT CPDEdit::OnContextMenu(WPARAM, LPARAM) {
return 0;
}

CPDEdit is the class derived from CEdit used to subclass the edit control. It traps the WM_COPY, WM_PASTE and WM_CONTEXTMENU messages and simply ignores them. Within your Dialog class change the type of control from CEdit to CPDEdit:

// CEdit m_edit;
CPDEdit m_edit;

And in the InitDialog() function subclass the control:

m_edit.SubclassDlgItem(IDC_EDIT, this);

Note that if you are using DDX with a control type then you don't need to call SubclassDlgItem because DDX internally calls it.