Can anybody recommend a company who translates legal documents into spanish?
A certified translation is a translation accompanied by a signed statement attesting that the translation is accurate and complete to the best of the translator's knowledge and ability. Any translator or translation company may "certify" a translation.
That being said, you should talk to some of the law firms, especially those who market to the Spanish speaking businesses who they use.
Try contacting Judy Jenner:
Even though my language pair is very different from hers, I learn a lot from Judy (and Dagmar)