Whether or not maintenance is required to give notice before entering for non-emergency repairs depends on what your lease says about the subject. So to answer that question, you need to review your lease. If it is unclear to you, you need to present your lease to an attorney for them to review and interpret.
To protect yourself, you need to get a lock for your files.
Hope this helps.
~ Kem Eyo
The above answer is a general explanation of legal rights and procedures. It does not constitute legal advice. Nor does it establish an attorney-client relationship between the individual posting the question and the attorney providing the answer.