Simple: drag your selected text to the binder.
A new document is created, and you can place it where you want in the binder’s document sequence.
If you started from a locked document (cmd-opt-L), the editor continues to display the original document. Otherwise, the editor displays the new document.
This was covered in a previous thread, but as part of a different discussion, so it was a bit difficult to find, at least for my simple mind.