Try rebooting your device and check if the issue still persists. If the problem was related to insufficient RAM on your device, rebooting will resolve the issue.
If it doesn't, please try reinstalling Printer Pro, as it should prevent the app from crashing again. To do that follow the next steps:
If reinstallation didn't resolve the issue, please send crash log to our Support team. To find Crash Log:
Open iOS Settings > General > About > Diagnostics & Usage > Diagnostic and Usage data > (for iOS 8 Settings > Privacy > Diagnostics & Usage) and copy the contents of the tab with "Printer Pro" or "crash" in the name > paste into the email message to us.