If a user is adding annotations to a pdf file and Okular closes without saving the file, the annotations are permanently lost and cannot be recovered. This can happen if the user just forgets to save them, or Okular or the desktop or the OS crashes / freezes. I've lost annotations by simply forgetting to save them, or when Linux was unable to resume properly from sleep. Adobe reader automatically saves annotation changes to a temperoary file every X minutes (usually 5) and can recover unsaved changes the next time the document is opened. This would be  avery useful feature for Okular and can save users a lot of lost work.

Reproducible: Always