You can also use key combinations to copy and paste: Windows: Ctrl + A to select all the text, Ctrl + C to copy, and Ctrl + V to paste. Mac: Command + A to select all the text, Command + C to copy, and Command + V to paste.
Or, before you add your text in the editor, you can paste it into an offline simple text editor, such as Notepad or TextEdit, and clear the formatting. Then, you can paste the text into the editor and format it as you want. More on the working in the editor.
While you add text to your course, you can protect against loss of work if an internet connection loss or software error occurs. You can type in an offline simple text editor, such as Notepad or TextEdit, and then copy and paste your work into your course.