Hi iang_106,
Convert > Text to Default Formatting will work for all selected documents, you’ve probably just missed a step.
See this thread for step by step instructions: [url]How to set default text formatting for whole project] It was written for v1.9, but should still hold true.
Do it first for your main manuscript in the Draft folder, then once you’ve got the steps figured out, do it for any other folders you like,
I recommend you make a zipped backup of your project prior to any big change like this. Undo will not undo it.
Best,
Jim