Is it possible to use the icons that apple shows for attachments like PDF's or Doc's in the mail app just generally in any app? If so where can I find them and is there a special way to add them into the app?
I can't speak for whether or not usage of the icons is allowed. However, they are accessible. Just download 0xced's iOS-Artwork-Extractor and run it on the simulator. It will prompt you for a to save the images, and once you confirm, EVERY image from within the iOs simulator from which you ran the project will be dumped into a folder on your desktop.
From there all you have to do is navigate around to find the images you need. They are organized by framework.