Activating Nitro Pro 9 for "free" through third-party serial numbers is not recommended due to significant security risks and legal implications. Nitro Pro 9 is a discontinued "sunset" product, meaning it no longer receives security patches or official support from Nitro PDF. Methods to Access Nitro Pro Legally

Risks of Using Free Activation Codes or Serial Numbers

is an older version. Official activation servers for versions 11 and older have been shut down.

No Security Updates: Cracked software cannot be updated. This leaves your system vulnerable to security flaws that the official developers have already patched in legitimate versions [4].