If you ever have the need to hack or crack the trial period on OPrint – an airprint relay / proxy / print server for Windows then here is how.

Quit OPrint
Delete the following registry keys and their sub-values.
HKLM\SOFTWARE\Wow6432Node\OPrint
HKCU\AppEvents\EventLabels\option
Delete the following file
C:\Windows\SysWOW64\config\settingenv
Re-open OPrint. The trial will be back to 30 days.

However – this software is reliable and fully worth paying for. These instructions might be ideal if you installed it and then forgot to test it before the trial period expired.