You can open an app that isn’t allowed to open by manually overriding the settings in Security & Privacy preferences.
In the Finder on your Mac, locate the eBook you want to open.
Control-click the app icon, then choose Open from the shortcut menu.
The app is saved as an exception to your security settings, and you can open it in the future by double-clicking it, just as you can any authorised app.
If it opens and comes up with ‘Blocked Plug-in’ please reinstall the Adobe Flash Player plugin with the following steps:
(Re-)installing the Adobe Flash Player
To install the Adobe Flash Player plug-in for the first time, or to update it to the latest version without checking for updates first, follow these steps: