The employment contract is a core document for the DNV under Law 14/2013. It must prove that you have been working for the company for at least three months prior to the application. The contract, or an accompanying certificate, must explicitly state that your position allows for remote work and that the employer authorizes you to perform your duties from Spain. The company must be located outside of Spain and have been operational for at least one year.
If the original document is not in Spanish, a sworn translation (Traductor Jurado) is mandatory. While the contract itself usually does not require an apostille, it is highly recommended to provide a Certificate of Good Standing or a Mercantil Registry excerpt for the company, which might require legalization. Regarding social security, if there is no bilateral agreement (like with the UK or Russia), the applicant must register as an 'autónomo' (RETA) in Spain. In this case, private health insurance is not mandatory once registered, as RETA provides access to the Public Health System (SNS). Common mistakes include failing to mention the 'remote' nature of work or having a contract that doesn't meet the minimum salary requirement (200% of the Spanish SMI).