how to lock or protected vba file in vb.net

If you wish to protect the workbook from being opened and/or read-only then in the Save As dialog box, click the Tools drop-down to the left of the Save button and specify the password for opening/allowing modification.

This can be achieved in VBA using something like the following:

ActiveWorkbook.SaveAs Filename:="C:\Users\John Mc Hale\Documents\Protect.xls" _
        , FileFormat:=xlExcel8, Password:="password", WriteResPassword:= _
        "password", ReadOnlyRecommended:=False, CreateBackup:=False