Before fixing the issue, it helps to understand why it happens. Apple has increasingly tightened security with features like Gatekeeper and XProtect. These systems are designed to prevent malware, but they often have "false positives"—flagging legitimate, niche tools like EPUBoor as suspicious because they lack an expensive Apple Developer Certificate.
Best for: App crashes immediately after opening.
Sometimes the download and installation succeed, but the app crashes immediately upon opening.
Epubor often updates faster for Windows than Mac. If you are on an Mac, try:
