How do I retain my photo edits when opening the files in other apps?
Assuming you're using iPhoto for iOS (please clarify):

Applications can only access photos stored in your iOS device's Camera Roll. When you edit a photo in iPhoto (and likely in other, similar applications), the app creates a copy of the photo and stores it within its own storage area, where other apps can't see it. In order to make the edited photos available to other apps, iPhoto lets you export one or more of your Edited photos in a variety of ways: select one or more photos and tap the Share button to see the options, which include sending the photo to your Camera Roll (where other apps can see it) and Open In... which lets you send the photo to a specific app.

I'll admit, this is somewhat inconvenient when you have a large number of photos, as even when selecting multiple, iPhoto limits you to selecting 100 at a time.