After opening Citavi you receive a message that the project is read-only.
Causes and solutions
Enter your license key for Citavi for Windows.
(Citavi 5 or earlier) You have not entered a license key in Citavi and have entered more than 100 references per project. Citavi Free has the complete functionality of Citavi for Windows, with one limitation: you cannot save if you have more than 100 references in all open projects. Please enter your license key.
(Citavi 6) You are either not logged in to your Citavi account or there is no license key linked to your account.
In Windows Explorer, right-click the Citavi project file and then click Properties. Click General and then clear the Read-only checkbox.
Extract the project by right-clicking the ZIP file and clicking Extract all. Open the extracted project file.