Since Microsoft To Do automatically syncs to Outlook Tasks, you can export all of your lists and tasks from Outlook.
To export your lists and tasks, just log in to Outlook.com with the same Microsoft account that you use to log in to Microsoft To Do.
Just select the cog icon to open your Settings and then select View full settings.
From the left navigation pane, select General.
Then, select Export from the middle navigation pane.
Finally, just select Export Mailbox to save all of your lists and tasks.
Please note that we're currently rolling this option out in stages, so it may not be immediately available to all of our users. If you don't see the option to export just yet, please bear with us while we finish rolling it out.