You do not need to be online to continue working on a cloud project. There are three situations that can occur:
Your Internet connection was interrupted while you were working on a Citavi project.
You can continue working and close your project when you're done. As soon as the Internet connection is available again, Citavi will synchronized your changes with the Citavi Cloud.
Your Internet connection was interrupted before you could open a Citavi project.
The cloud project does not appear in the list of recently opened projects. On the Welcome Screen, click Open project. You'll find your project on the Cloud tab. Click the project name to open it.
You're connected to the Internet but you temporarily don't want to save changes to your cloud project.
If you're working on a Citavi cloud project over an expensive Intenet connection (for example, a metered connection over your smartphone), you might want to work offline. To do so, on the Citavi Welcome Screen, click the gear symbol. Then, select Go offline to work in offline mode. Once you're connected to a normal Internet connection again, select the option Go online.
If you're working offline, you can't attach PDF files to a reference, add image or file quotations or add cover images.