ok, so I took bits of codes from the internet and managed to get some stuff to work but it only works on the first page and I would like that to be done on every page. I'm sure it's a noob mistake but just haven't found the answer.

The idea is that it writes the filename with a barcode font and the line after the page number, I put it in two different loops to have two different fonts (hoping that it makes sense).

    for (var p = 0; p < this.pageNum; p++);
var cMyText = event.target.documentFileName.replace(/\.pdf$/i,"");
event.target.addWatermarkFromText({
    cText: cMyText,
    nFontSize:10,
    aColor: color.black,
    cFont: "LibreBarcode39Text-Regular",
    nHorizAlign:app.constants.align.left,
    nHorizValue: 36,
    nVertAlign:app.constants.align.top,
    nVertValue: -3,
    nStart: p
})
for (var s=0; s<this.pageNum; s++);
var cMyText = "\nPage " + (s+1) + " of " + numPages;
event.target.addWatermarkFromText({
    cText: cMyText,
    nFontSize:8,
    aColor: color.black,
    nHorizAlign:app.constants.align.left,
    nHorizValue: 36,
    nVertAlign:app.constants.align.top,
    nVertValue: -10,
    nStart: s

})