JS has no access to the tags information of a PDF.
As noted you cannot access the "Tag" of a PDF but you can access the meta data of a PDF and one of the items recorded in the meta data is the "producer". This meta data tag is supposed contain the name of the program that produced the PDF. One can access this through the "info" property or the "metadata" property of the doc object.
var cProducer = this.info.Producer; // get the producer application for this PDF;
console.println("This PDF was created by " + cProducer);