I have done something like this before, when I needed to export the json (not saying this is a recommended approach as there might be a proper API you can use).
I did something like...
var currentPage = _pageDataContextRetriever.Retrieve<TreeNode>().Page;
var json = currentPage.GetStringValue("DocumentPageBuilderWidgets", string.Empty);
// Then deserialise this to a custom c# class that represents the editable area/sections/zones/widgets
var pagebuilderData = JsonConvert.DeserializeObject<CustomPageBuilderModel>(json);