This filter allows you to add columns and modify data of the CSV exported in the Caldera Forms admin entry viewer.
This filter was added in Caldera Forms 1.5.3.
Add Column To Caldera Forms Admin CSV
Similar Filter For Attached Emails
This filter does not modify the CSVs attatched to Caldera Forms emails. Use caldera_forms_email_csv_data instead.
Where Does This Code Go?
When using WordPress hooks to customize Caldera Forms or other plugins you should not modify the plugin files, or you will lose your changes when you update the plugin. Instead you should create a small plugin to hold the custom code. It's easy, learn how here.
Technically you can add the custom code to your theme's functions.php, but then you will not be able to change your theme and keep these customizations.