iPhone open default application for file type

I am writing an app that will be downloading user's documents from a remote source. once my app has this document I want to open it in the default application. (.PDF) In android it was simple, but I cant seem to find any resources for iPhone.

How do I open the default application with the file?

EDIT

The file on the remote source is not a url. it开发者_开发百科 needs to be downloaded through a web-service. I will either be saving the file to disk or trying to open it from memory.

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You are probably looking for UIDocumentInteractionController. Read this guide as well for more information.