With iOS 9, Apple has finally made it easy to attach files to emails you compose on your iPad. Instead of going to individual apps and hoping they will allow you to share a file via email, iOS 9 allows you to write your email and then attach a file from your iCloud Drive (which is by far the easiest way to manage your files across all of your devices). To add an attachment simply long press anywhere on the email until the magnifying glass shows up. Let go and a menu of options will come up, one being "Add Attachment." Tap on that and a window for your iCloud Drive will pop up. You can add a file from here or you can tap "Locations" in the top left corner to find files elsewhere on your device (this option will only appear if you do have files in other apps).