PDF Embed API: Store and retrieve annotations

Hi there,

I'm new to this API, so this is most certainly a beginners question.

I want to use the API for a very simple application: Embed a PDF on my website and allow any user to annotate the file and also to see all existing annotations. While embedding the file works just fine, I can't figure out how to store and retrieve user annotations. I understand that user annotations are to be written to JSON-files but how do I create them in a user session? 

I went through the examples on GitHub (https://github.com/adobe/pdf-embed-api-samples/tree/master/More%20Samples/PDF%20Annotations%20APIs) but wasn't able find a solution for my problem.

A link to a tutorial or some code example would be very helpful!

Thanks!