how can I obtain a license file for quartus prime lite, that enables the design security feature? Thanks

Done, kindly generate your license file in Self Service Licensing Center. Only the license administrator can re-generate the license file.

Guidance: https://fpgasupport.intel.com/AlteraLicensing/license/index.html --> Licensing Center Home --> Computer and License Files --> Select a computer to generate a new license file.

Link to demo: https://www.intel.com/content/www/us/en/programmable/support/training/demonstrations/online/licensing/onl-licensing.html