This is because you are doing it wrong. GetObjectjust opens the object with default behavior. You must create an object Word.Application:
my $word = Win32::OLE->new( 'Word.Application' );
Then use the Documentscollection method Openwith the specified parameter ReadOnly. For example:
$doc = $word->Documents->Open( { FileName => $document_path,
, ReadOnly => 1
} );
Read http://msdn.microsoft.com/en-us/library/bb216319.aspx for syntaxDocuments.Open