Law 39/2015
Article 16. Records
"4. The documents that the interested parties send to the public administration bodies can be presented:
a) To the electronic register of the Administration or body to which they are addressed, as well as to the other electronic registers of any of the subjects referred to in article 2.1.
b) At post offices, as established by regulation.
c) To the diplomatic representations or consular offices of Spain abroad. d) At the registration assistance offices.
e) In any other established by the provisions in force. [...]"
5. The documents presented in person before the public administrations must be digitized, in accordance with the provisions of article 27 and other applicable regulations, by the registration assistance office in which they have been presented for its inclusion in the electronic administrative file, and the originals must be returned to the interested party, without prejudice to the cases in which the rule determines the custody by the Administration of the documents presented or it is mandatory to present objects or documents in a specific medium not susceptible to digitization.”
Article 28. Documents provided by those interested in the administrative procedure.
"1. Those interested must provide the administrative procedure with the data and documents required by the public administrations in accordance with the provisions of the applicable regulations. Likewise, those interested can provide any other document they deem appropriate."