Law 39/2015
Article 16. Records.
"[...] 4. The documents that the interested parties address to the organs of the public administrations can be presented:
[...] b) At post offices, as established by regulations.
[...] 5. Documents submitted in person to public administrations must be digitized, in accordance with the provisions of Article 27 and other applicable regulations, by the registration assistance office in which have been submitted for incorporation into 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 submitted 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. Administrations shall not require interested parties to submit original documents unless, exceptionally, the applicable regulations provide otherwise.
[...] 4. If, exceptionally, and in accordance with the provisions of this Law, the Administration requests the interested party to submit an original document and it is in paper format, the interested party must 'obtain an authentic copy, in accordance with the requirements laid down in Article 27, prior to its electronic submission. The resulting electronic copy must expressly reflect this circumstance.
5. Exceptionally, when the relevance of the document in the procedure so requires or there are doubts arising from the quality of the copy, the administrations may request in a reasoned manner the comparison of the copies provided by the interested party, for which which may require the original document or information to be displayed. "