Hello
There are several ways you can do it.
You can open a separate writing app side by side with MarginNote 3. GoodNotes and Notability are good choices.
You can also click the three dots at the top right corner and choose the "leave blank" function. That way, you will be able to increase the margin of your document and write on the margin.
We are also working on something exciting that might help you. Stay tuned.
Kind Regards,
MarginNote-Sushi
Support Team