May I start this off with a short note.
This post is about how to purchase a Spanish registered car. I have never  done this with the intention of importing a Spanish car into any other country. Having lived in Spain for many years I can assure you that a clerk in an office may just want to make up some sort of regulation which he knows about. Advise is go along with the flow.
Copies of any documents may have to be in Spanish and you may need photo copies of them. The government offices you are visiting in order to clear the paperwork usually do not copy any of your documents for you. They will know whee there is a machine nearby, usually a newspaper/book suppliers or post office.
This has been written as a guide and must not be taken as any legal framework.
 
Lets get down to it-
 
 
Documents:
Provided for the vechile:
 
Vehicle registration certificate(s). Comes in two parts. One is known as Permiso de circulación.
Front and back:

Inside:

The second is Ficha técnica del vehículo.One side:

The other side:

These have changed over the years but these are the ones you would more than likely encounter when look at Spanish Shite. ITV inspections are no longer stamped they now add stickers to the document with a fail or pass.
The windscreen sticker which states the car has passed its annual roadworthy test. Known as I.T.V. (Inspección Técnica de Vehículos).

 
The sticker colour changes every year. Normally issued for 12 months, but hire cars, taxis and buses plus HGVs are issued for every 6 months. The year end is indicated and the month is removed with a hole punch. No car can be driven on Spanish roads without a valid test. Not even to the test station. The new regulation is that the Spanish can now get a test  done up to one calender month before the end of year of the test cert.
 
 
To sum up that makes  3 sheets of paper and a little sticker.