Once the path is set, Altium will "see" the extensions available in that folder as if they were live on the web. Stay in the tab. Click on the Purchased or Installed sub-tab.
Ensure you have the main offline installer for your specific version of Altium Designer. Extensions are often version-specific. altium extension offline install
If the extension doesn't appear, verify that the offline package version matches your installed Altium Designer build (e.g., AD24 files won't work with AD23). Once the path is set, Altium will "see"
Click the button (the gear icon) in the top right corner. Ensure you have the main offline installer for
Under the section, locate the Offline Installation option. Check the box for Use a local installation service .
Copy the entire installation package (which includes the extensions folder) onto a secure USB drive or a dedicated internal network share that the air-gapped machine can reach. Phase 2: Configuring the Local Installation Service
Even with extensions installed, remember that your Altium License must also be handled offline using a .alf license file, as the software cannot "phone home" to the Altium On-Demand license server. Why Install Offline?