How to read and set private fields without improving performance in C #?

RavenDB can serialize all public, private, and protected properties on any given C # object, even without any serialization attributes.

I know this can be done with reflection, but it will have some performance issues. Are there other more effective ways to achieve this?

Using built-in serialization in .NET requires annotations or the implementation of some serialization interfaces, while RavenDB can serialize any given object to and from JSON.

I'm more interested in the technologies that it uses, rather than RavenDB.