This error means that you need to re-register your license:

  1. On your iPad, go to the PDCViewer app and tap the gear in the top left corner.
  2. On the settings screen, choose the "Remove Keystore" option and confirm your choice.
  3. Open your Safari app and return to the Download Center on our website.
  4. Skip to Step 3: License Registration, select "Register this device" next to your iPad, then choose the option to "Open in PDCViewer."
  5. Tap on the latest license listed in your PDCViewer's licenses area and you should receive a successful registration message.

You should now be able to open files on your iPad.