Please find below the certificate document to be presented when necessary to the customs authorities at Bilbao airport
You can find here the same certificate in Spanish as well as in English to better understand the contents.
I suggest you to use the "Spanish certificate" to be showed at the Spanish border police if neccesary.
Please, complete the personal data as well as the airgun.
If you heve any question , please, don't hesitate to ask me for.