Inability to add memo

Hi all,

I have a problem with adding memos on the document (MS Word) which is locked and has only some spaces allowed to fill in. I could not add memos at all eventhough I tried to add memos for the filled information in the editable spaces. 

Anybody knows how to solve this issue?

I really need to know to add review comments for written information on the protected form.

Thank you in advance.