What steps should I follow to legalize documents for a Non-immigrant O-A visa application in Spain?

I got my first "retirement" visa at the thai embassy in Madrid. What they are asking is to legalize a photocopy of the original documents by a notary, not the original documents. So, what the notary will do is to compare the original documents with the copies and then stamp the copies.

A notary, at least in the US version, is someone who has the legal authority to verify the person signing the document is, to the best of the notary’s ability, that person. For that reason you cannot go to a lawyer or anyone else after the fact and ask them to notarize a signature. Also, a bank or other entity cannot use their notary to notarize their signature - they would essentially be notarizing their own signature.

Take original documents and I'd to a lawyer he will notarise documents

are u applying for a non o cause of ur going to retire in Thailand ( over 50)? If so just apply for a single entry Non O visa ( valid for 90 days) and once in Thailand get a 1 year extension..

no Medical, no police clearance,no bank books needed

I used my translation of the Thai Embassy in Madrid to get this outcome: Visa No - I n migrant and "OR - TO" This type of visa do may be granted to applicants who are 50 years of age or older and wish to stay in Thailand for a period of less than 1 year and do not intend to to work. Holders of this type of visa can stay in Thailand for 1 year. Is t erminantemente prohibited any type of employment. REQUIREMENTS  The applicant must be 50 years of age or older (as of the filing date of the request).  Not to have the entrance to the Kingdom prohibited according to the Immigration Law of 1979 (Immigration Act B.E. 2522) .  No criminal record in Thailand or in the country of origin or residence.  Be a citizen or resident of the country in which you are presenting application.  Not having any of the forbidden diseases (such as Leprosy, tuberculosis drug addiction, elephantiasis, syphilis, third stage) as indicated in the Disposition Ministerial No. 14 of the year 2535 E.B. DOCUMENTATION REQUESTED  Passport original and two copies with a validity of not less than 18 months.  3 Forms visa application do duly c Completed and signed .  3 passport size photos in photographic paper , front without sunglasses and with the uncovered head (taken at most 6 m eses before).  3 Form s of d atos p ersonal "OR - A "duly completed I not read that all documents need to be legalized. But it is just a translation, your Spanish should be much better than mine %20Immigrant%20O-A%20para%20web.pdf

Did you ask your Embassy if it is possible to legalize your US documents to use in Spain?