TextEdit opens a new document in rich text mode, but you can easily convert the document to plain text. You would want to do this when you need to strip out formatting to input data into programs that don't support (or translate) rich text easily.
1. Open TextEdit and then open the document in TextEdit by clicking on Open in the File menu.
2. Click on Format, then Make Plain Text.
3. A window will pop up asking if you want to convert the document to plan text. Press OK.
4. A window will pop up asking if you want to either overwrite the document, or duplicate the document. When in doubt, you can always choose the Duplicate button, and that will pop up a separate window with a copy of the document in plain text. If you press Overwrite, then the document will be changed to plain text.
Here is the difference between the original rich text and plain text!