Add "Date Printed" on a LOT of labels

I have a bunch of bottle labels in .pdf format. Currently I am editing each individual label to place two fields on them. The fields are "MonthPrinted" and "YearPrinted." Once I place the two fields on the label I add the following code to the Document Action "Document Will Print"

     var f = this.getField("MonthPrinted");

     f.hidden = false;

     f.value = util.printd("mmm", new Date());

     var g = this.getField("YearPrinted");

     g.hidden = false;

     g.value = util.printd("yyyy", new Date());

This works fine, but I now need to redo about 4000 labels and I am looking for a way to do this as a batch process so I don't have to add this code to each new .pdf file. In a past life I was a programmer (in assembler language, which tells you how old I am) but I am not familiar with newer languages and scripts.

Since this is for a business, I am willing to pay someone to assist me with this humongous task.