Where does my exported document go?

Back to your desktop via iTunes when you sync. Look on the Apps tab when the iPad is connect, and scroll down - you'll see a pane to control syncing from iPad apps that support it

The iPad OS doesn't give you access to the file structure, so there's no "Documents' folder or equivalent. I suppose that the app (Pages in this case) tracks the document

There is a shared folder on the ipad that you can see fromapps on the iPad, and from iTunes on the computer.
You would add the file to this folder using iTunes. Then on the iPad, you import that file into the actual apps file list. This makes a copy in the sandboxed area for the app. A copy stays in two locations now. One original copy in the shared folder, one being edited in the app.

If you mess up the edited file, you can delete it and reimport from the shared fielder.

If you want to keep the changes on the iPad you can export back into the shared folder which you can then see on iTunes.

Be careful, make sure that if your about to delete an app, you first sync and copy all files to the desktop before deleting it. I lost a bunch of files in numbers because it apparently deletes all files associated with the app.

Jason