The best way to download the free version of Avast antivirus is by downloading it from the official Avast website. The best part is, you can download the free Avast antivirus software for any platform you want. You can easily get the license key for Avast from its official website if you follow the given instructions there carefully. Now, you ask how to download Avast antivirus full version for free; then the answer is to go to Avast official website and click on the 'Free download' option. Once the downloading is over, open the file and execute the instructions there carefully to finish the installation process.