A 12-month Pre/Post license is typically used in conjunction with an Intermittent simulation license. But there can only be one active Simerics license on a computer at a time. If the Pre/Post license is installed on a different computer than the Intermittent simulation license, there won't be any conflicts between the licenses and you do not need the information below.
But, if you want to use the same computer for your Pre/Post license and your simulation license, you will need to do some manual management of the .lic license files. For example, if you have completed one of your Intermittent simulation licenses and then want to use your Pre/Post license, just start Simerics and it will give an error since you don't have an active license. Select "Activate Node Lock License" and enter your Pre/Post license key. Then your Pre/Post license will be active and you will be able to load any .spro project files as well as .sres results files, and save images, plot the data, create animations, etc. (everything except actually run a simulation).
When you're ready to run some simulations, you will need to activate another of your Intermittent simulation licenses. To do this, you first need to deactivate the Pre/Post license. Look in the folder C:\ProgramData\Simerics for the latest *.lic file (if you don't see that folder, you should look in C:\Program Files\Simerics). This will be your Pre/Post license. Change the extension on the file to something that's easy to understand when you come back to it; for example, change it from .lic to .prepost.
Now start Simerics. It won't recognize a file with the extension .prepost, so it will give a license error. Select "Activate Node Lock License", and type in the license key for your Intermittent license.
At the end of the 30 days, change the extension from .prepost back to .lic on the Pre/Post license file, and change the extension on the now-expired .lic file for the Intermittent license from .lic to .old to make it clear to yourself later that it is an expired license. You could even change it to .2 if it was the second of your Intermittent licenses, which would help you to keep track of how many Intermittent licenses you have used.