FileIOPermission isAvailable = new FileIOPermission( PermissionState.None); 
try
{
isAvailable .SetPathList( FileIOPermissionAccess.Read, fileName);
isAvailable .Demand( ); // does file permit shared reading?
Console.WriteLine( "{0} is O.K. to read.", fileName);
}
catch ( SecurityException _se)
{
MessageBox.Show( _se.Message);
}