Storing C# application data without a database. What to choose?

Question

Database

For a long time I wrote applications for myself on the WPF + Entity bundle, but now the task has arisen to store application data (5-8 database tables with complex relationships) without a database.
Who uses what, tell me please? Do not offer XML, since the database data must be protected from editing with a notepad)

Answer 1

Why not use at least SQLite? Lightweight, you can't change it with a notepad.

Answer 2

Store in flat files. Encrypt them to protect them from editing with notepad.

Answer 3

RavenDB: embedded mode (embedded in the application, does not require additional tools to be installed). They did everything so cool and convenient that it’s hard to change to something else later.
ravendb.net