Demfilz Custom Forms is a form builder. To do its job it has to store what visitors type into your forms. This page says exactly what that means.
.myshopify.com domain, the offline access token Shopify issued at install (encrypted at rest), your store name, contact email and primary domain.It does not sell, share or analyse the data, does not use it for anything but showing it to you and sending the emails you configured, and only writes to Shopify (customers, companies) when you switch that on for a form and grant the permission. There is no tracking and no telemetry.
Notifications are sent from the app's sending address with your store's address as the reply-to, or from your own SMTP server if you configure one. They contain the submitted values and signed, expiring links to any files.
customers/redact: every entry and file belonging to that customer (matched by customer id or email) is deleted.customers/data_request: everything held about that customer is sent to your store's notification address as a JSON file, for you to pass on.shop/redact and uninstalling: your store's entire record, entries and files included, is deleted.Entries are kept until you delete them, the form's retention window passes, your customer is redacted, or you uninstall the app. Files are stored under random names and served only through short-lived signed links.