A Sworn Translation can only be done by a Sworn Translator appointed by the Ministry of Foreign Affairs (MAEC).
The translation must include a statement from the Sworn Translator certifying that it is a true and complete translation, with the date, signature and stamp of the Sworn Translator.
In addition, a copy of the original must be attached, which must be dated and stamped on all its pages.
More about sworn translation:
Sworn translations are official translations signed and stamped by a sworn translator recognised by the Spanish Ministry of Foreign Affairs and Cooperation, and these are legally valid for use by various public bodies within Spain and abroad.
I mainly provide sworn translations for individuals (birth, death, and marriage certificates, police background checks, academic certificates, university degrees, wills and passports, for example), but also for companies and law firms.