Isumsoft is a commercial product (typically $39–$49). There is no "free" legal version that unlocks full RAR recovery. The company relies on sales revenue to develop the software. Any claim of a fully functional "best free" version is a lie designed to infect your machine.

If you cannot purchase the full version, consider these free, legitimate, or open-source alternatives:

Repeating for emphasis – there is no legal, safe, free registration code. Any website promising one is either distributing malware or running a survey scam. The only "free" version of Isumsoft is the 3‑character trial, which is essentially useless for real recovery.