Saveing tabs and content when closing app

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C#

Im making a small app in which i can write telephone notes and other stuff at work.
Im using a tab control to add different types of tabs and everything is working as intended.
The thing is, id like to be able to save all the tabs and their contents when i close the app (or whenever i choose) so that i can i.e. restart the computer and such without loosing any notes. If anyone can point me in the right direction that would be great. Thanks!