If a user who only has Read permissions has the document open, Word 97 doesn't properly use your NTFS permissions.
If you configure the document to require a password for modifications, Word 97 will properly use NTFS permissions, prompting a user who has Change permissions for a password, before opening the document, but will open it without the password prompt for users that don't.
To configure the document to use a password:
1. In Word 97, on the File menu, press Save As.
2. Press Options.
3. Type the password you want to set into the Password to Modify ... box and click OK.
4. Type the confirming password and click OK.
5. Press Save.