Open-In button

There are many apps that allow you the ability to export particular files into another app for viewing.
Example: I have a PDF in an email someone sent me. When I read it on my iPod, there is an option to open that PDF in another app. I choose an app I bought called "Documents Pro". From there I can read it and arrange it in folders and such.

If you could add that button in there, I can upload it to my Dropbox account, download from my device to my computer, and so many other things.