There are no files to download and update, everything required for extended functionality already exists in the main application.
If the addon is not registered, it works in DEMO mode - you can do everything, but you will not be able to import more then 20 items at once.
To unlock its functionality, you have to purchase the appropriate license and register this extension.
Registration requires license key. See this article regarding registration issues. You can reset addon's license (due to hardware change etc) in the same way as the main software license.
The PDF Catalog Creator registration:
After purchase all customers receive email notification with registration information. You may find License Number (key) there.
Go Settings -> "Preferences" sector of Store Manager and activate the "Addons" tab to see the list of available addons.
As you can see in the illustration below, the addon is unregistered now.
There are other possible registration statuses:
Unregistered - the addon is in DEMO mode
Registered - the addon is registered and fully-functional
Verifying... - the software is checking the registration information
3. Click the registration status to see the PDF Catalog Creator registration window. Enter your License Key and press [OK]:
4. Store Manager will check the License key and return the addon's status. If activation is successful, you will see a green colored text “Registered”
Now the PDF Catalog Creator addon is registered.