Law 39/2015
Article 16. Records.
"[...] 4. The documents that the interested parties send to the public administration bodies can be presented:
[...] b) At post offices, as established by regulation.
[...] 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 that have been submitted for 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 of the submitted documents by the Administration or it is mandatory to present objects or documents in a specific medium that cannot be digitized."
Article 28. Documents provided by those interested in the administrative procedure.
"[...] 3. The administrations must not require the interested parties to present original documents, unless, exceptionally, the applicable regulatory regulations establish otherwise.
[...] 4. If exceptionally, and in accordance with the provisions of this Law, the Administration requests the interested party to present an original document and this is in paper format, the interested party must obtain an authentic copy, according to the requirements established in article 27, prior to its electronic presentation. The resulting electronic copy must expressly reflect this circumstance.
5. Exceptionally, when the relevance of the document in the procedure requires it or there are doubts arising from the quality of the copy, the administrations can request a reasoned comparison of the copies provided by the interested party, for which which may require the original document or information to be produced. "