To protect your TextEdit documents from being changed, you can make them “read-only.” This is useful for documents such as “Read Me” files, license agreements, and any other documents you don’t want the reader to be able to edit.
To mark a TextEdit document as read-only:
Open the document in TextEdit and choose Format > Prevent Editing.
To make changes to a read-only TextEdit document that you own:
Open the document and choose Format > Allow Editing.
You can also control access to your document by locking it or by setting permissions for it.