Upon first launch user is asked to provide the license file (with a extension *.license). The license file itself contains all the information about supported package which allows for offline use of the software.
The license file can be downloaded from: https://br-ag.eu/products/atome-particles/download-license/. After providing the license key there a particles.license file will automatically start downloading, that then can be used to activate the application.
Important: the application will always refer to the licensing file while it's in use, so make sure that the file is always accessible by the application itself, if the file is not accessible or missing, the application will ask the user to point to another one.