How do I install Adobe Premiere Elements on a computer that's isolated from the Internet?
Using Google, a popular internet search engine, the Adobe help page that discusses this topic is easily discovered.  In particular, it explains:

You must connect to the Internet when you want to install Adobe Creative Cloud apps, such as Photoshop and Illustrator. Once the apps are installed on your computer, you don’t need an ongoing Internet connection to use the apps.
You can use the apps in offline mode with a valid software license for a limited period. The apps attempt to validate your software license every 30 days. You receive a reminder to reconnect to the Internet to validate your license...

You can read more details on that web page and decide whether or not your online/offline behavior fits within those parameters or not.