Can you clarify a bit more on what you are wanting to do?
As I understand it, your workflow involves retrieving DiagnosticReports, and you want to display the actual content of each DiagnosticReport's presented form inside your app?
To do this, you would just need to parse the DiagnosticReport response to get the presentedForm.url and presentedForm.contentType values for each diagnostic report. Then fire off a new request to the url with an Accept header set to the content type. The results from that Binary request will be the content of the DiagnosticReport's presented form. You can display the results in your app.
Please let me know if I'm understanding the situation correctly!