You can use the Document Viewer in the app store to display your documents in your forms.
As for displaying according to type. You can create an Enumeration of the types of documents which you set accordingly when committing the document. In your overview page you can create a listview (or something similar) for every type of document, which retrieves the documents from the database either by microflow or xpath, where you check if the document is of that type.
Retrieve your entity by Xpath
[documentType = ' Invoice']