Enabling Encryption in a file backup job
In order to implement Encryption in a file backup job, the file backup job would be required to have been originally created via the "Backup" tab. You will open that backup job via the "Backup" tab (alternatively you can via the Schedule tab locate the job, right-click on it, and choose "Modify Job"), then click "Open Job" and locate that backup job and select it from the list, once the backup job is open then click the Settings button on the bottom right of the screen. There you will find an Encryption tab to click on. The Online Help topic for how to do this is at the web link here:
Backup Job Encryption - Topic in NovaBACKUP Manual
After enabling Encryption in your job make sure to then save the job. The next time the job runs it will be encrypted. In order to restore content from that backup set you will then utilize the Restore tab to locate that backup set by backup job name and date completed, and then choose which files / folders to restore completely. When you go to restore files or folders from the backup set via the Restore tab you will be prompted for the encryption key passphrase. Here is a video guide on how to utilize the Restore tab/function.