The DigiCert Certificate Utility is one of the best certificate tools out there. You can use it to generate requests and process new certificates or renewals, fix missing private keys, fix certificate chains that are missing certificates – from any vendor, not just DigiCert. If you’re a programmer, you can use this to sign files and batches of code.
You can find this little bit of magic, along with the rest of what it can do, right here
The utility doesn’t install, it’s just an exe that you run. Best of all, it’s totally free!