timestamp-pdf.js

// USING https://github.com/Hopding/pdf-lib

      // ADD PDF TIMESTAMP AFTER ANCHOR CLICK
      $(document).ready(function(){
        $("a").click(function(event){
          event.preventDefault();
          console.log("user clicked pdf link");

          file = event.target.href; // e.g. file = 'docs/example1.pdf';
          fetch(file) .then(
            function(response) {
              console.log('Fetched!');
              response.arrayBuffer().then(function(buffer) {

                // INSERT TIMESTAMP ----------
                const existingPdfDocBytes = new Uint8Array(buffer);
                const pdfDoc = PDFDocumentFactory.load(existingPdfDocBytes);
                const [helveticaFont] = pdfDoc.embedStandardFont('Helvetica');
                const pages = pdfDoc.getPages();
                const page  = pages[0];
                page.addFontDictionary('Helvetica', helveticaFont);
                const contentStream = pdfDoc.createContentStream(
                  drawText( (new Date()).toISOString().slice(0, 19) , { 
                    x: 200,
                    y: 800,
                    size: 16,
                    font: 'Helvetica',
                    colorRgb: [0.95, 0.26, 0.21],
                  })
                );
                page.addContentStreams(pdfDoc.register(contentStream));
                const pdfBytes = PDFDocumentWriter.saveToBytes(pdfDoc);
                
                // DOWNLOAD IMMEDIATLY ----------
                download( pdfBytes, "textUInt8Array.pdf", "text/plain" );
                
              });
            }
          ).catch(function(err) {
            console.log('Fetch Error :-S', err);
          });
        });
      });