Hello @Andrés_Vilensky,
Not sure if this is exactly what you are looking for but there are various tools that directly integrate with Asana such as [Docusign](DocuSign + Asana • Asana.
Now I know there are also some that you don‘t pay monthly for but can get a cheap lifetime deal such as Grabsign for example (have used it before is okay in terms of features for the price). Now those I am not sure however if you can connect them with Asana somehow.
Also here is an existing feedback request thread that you might be interested in upvoting.