Manuscrito literally translates to "manuscript", like an old book or document written by hand. It's a very unique and poetic word to find in a pop song.
In 'Despacito', the line "hacer de tu cuerpo todo un manuscrito" (to make your body a whole manuscript) is a beautiful metaphor. It suggests exploring and leaving a mark on a lover's body as if writing a unique story, turning an intimate moment into a work of art.
This song is all about taking your time with seduction. Luis Fonsi spots someone he's instantly drawn to, singing, "Tú, tú eres el imán y yo soy el metal" (You, you are the magnet and I am the metal). He knows something is going to happen, but the whole point is to move slowly, which is what "Despacito" means. He wants to savor every single moment, from whispering in their ear to breathing in the scent of their neck.
He gets incredibly poetic and intense with his descriptions of this slow-burn passion. He sings about wanting to "firmar las paredes de tu laberinto / Y hacer de tu cuerpo todo un manuscrito" (sign the walls of your labyrinth / and make your body a whole manuscript). It's a powerful way of saying he wants to explore every part of his partner. The song builds to a climax on a beach in his native Puerto Rico, where he wants to be so passionate that even "las olas griten 'Ay, bendito'" (the waves scream 'Oh, blessed').