The need to decode IONCube-encoded files might stem from various scenarios:
Attempting to decode ionCube-protected software without permission violates copyright laws (DMCA Section 1201 in the US; similar laws in EU and elsewhere). If you succeed (you won't) and redistribute the decoded code, you face severe financial penalties.
From a technical standpoint, decoding IonCube 13 files without access to the original encryption keys or a legitimate decoder provided by the software owner is extremely challenging, if not practically impossible, for several reasons:
For forensic analysis of encoded files (e.g., to check for backdoors in a purchased application), hire a cybersecurity expert who uses approved debugging tools. They can sometimes analyze behavior without decoding the source.