Once you've installed PadKeys as a keyboard under device Settings | Keyboard | Keyboards (see video), it should immediately start showing up in every app when you cycle through the options by pressing the Globe key.
HOWEVER, it does not always work this way:
- PadKeys will never be shown for password fields, due to security restrictions in iOS.
- Individual apps may choose to deliberately disable third-party keyboards for reasons of their own. For example banking apps often disable them everywhere.
- If you have a company-managed device, third-party keyboards may be locked out of managed apps.
- Sometimes, due to iOS bugs, some apps don't "get the message" right away that there is a new keyboard available. Ironically it's often Apple's own apps, like Safari and Mail, that have this problem.
In the last case, the first thing to try is to hold down the Globe key rather than tapping it. This will bring up a menu of keyboards and you should be able to select PadKeys from there. (If you don't see it, go into the main Settings | Keyboard | Keyboards again and make sure PadKeys is added.)
If even this doesn't get PadKeys showing up, the apps in question will "wake up" and start showing it eventually. Sometimes this process can be sped up by killing and restarting the app, or restarting the entire iPad. Other times, despite doing these things, it actually takes a couple of days. Do not despair though: generally once an app "sees" PadKeys for the first time, the problem will not recur.
We encourage reporting this problem directly to Apple, either via http://www.apple.com/feedback/ipad.html or via their bug reporter if you have a developer account.