You first need to install java. (run sudo eopkg it openjdk-11
If you run into any error, look at: https://discuss.getsol.us/d/6413-help-with-javajar-files/9)
Now, extract the binaries of the file. (you can download the following zip file here: if you don't trust me, then you can extract the .deb file, and follow along)
Next, unzip the file, now run the terminal and run: java -jar ~/Downloads/firma/usr/lib/AutoFirma/AutoFirma.jar
I'm not really sure if it runs the thing you asked, because I'm not spanish.
I hope this is what you were looking for: