Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Teams

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

I can't get unifying multiple pdf-lib examples to work for me. I want to do in the same function that I add a text and an image in an existing PDF. It keeps giving me mistakes, and I do not understand why.

const { degrees, PDFDocument, rgb, StandardFonts } = PDFLib
async function modifyPdf() {
  // Fetch an existing PDF document
  const url = 'https://pdf-lib.js.org/assets/with_update_sections.pdf'
  const existingPdfBytes = await fetch(url).then(res => res.arrayBuffer());
  // Embed the Helvetica font
  const helveticaFont = await pdfDoc.embedFont(StandardFonts.Helvetica);
  // Get the first page of the document
  const pages = pdfDoc.getPages();
  const firstPage = pages[0];
  // Fetch JPEG image
  const jpgUrl = 'https://pdf-lib.js.org/assets/cat_riding_unicorn.jpg';
  const jpgImageBytes = await fetch(jpgUrl).then((res) => res.arrayBuffer());
  // Load a PDFDocument from the existing PDF bytes
  const pdfDoc = await PDFDocument.load(existingPdfBytes);
  const jpgImage = await pdfDoc.embedJpg(jpgImageBytes);
  const jpgDims = jpgImage.scale(0.25);
  // Get the width and height of the first page
  const { width, height } = firstPage.getSize();
    firstPage.drawText('This text was added with JavaScript!', {
       x: 5,
       y: height / 2 + 300,
       size: 50,
       font: helveticaFont,
       color: rgb(0.95, 0.1, 0.1),
       rotate: degrees(-45),
        // Add a blank page to the document
 firstPage.drawImage(jpgImage, {
    x: firstPage.getWidth() / 2 - jpgDims.width / 2,
    y: firstPage.getHeight() / 2 - jpgDims.height / 2,
    width: jpgDims.width,
    height: jpgDims.height,
  // Serialize the PDFDocument to bytes (a Uint8Array)
  const pdfBytes = await pdfDoc.save();
        // Trigger the browser to download the PDF document
  download(pdfBytes, "pdf-lib_modification_example.pdf", "application/pdf");
Error:
error:  VM3133:14 Uncaught (in promise) ReferenceError: Cannot access 'pdfDoc' before initialization
at modifyPdf (:14:29)
Basically, you are using pdfDoc before declaring it. So, just bring
const pdfDoc = await PDFDocument.load(existingPdfBytes);
to the top before using it for the first time.
Final Code:
const { degrees, PDFDocument, rgb, StandardFonts } = PDFLib
async function modifyPdf() {
  // Fetch an existing PDF document
  const url = 'https://pdf-lib.js.org/assets/with_update_sections.pdf'
  const existingPdfBytes = await fetch(url).then(res => res.arrayBuffer());
  // Load a PDFDocument from the existing PDF bytes
  const pdfDoc = await PDFDocument.load(existingPdfBytes);
  // Embed the Helvetica font
  const helveticaFont = await pdfDoc.embedFont(StandardFonts.Helvetica);
  // Get the first page of the document
  const pages = pdfDoc.getPages();
  const firstPage = pages[0];
  // Fetch JPEG image
  const jpgUrl = 'https://pdf-lib.js.org/assets/cat_riding_unicorn.jpg';
  const jpgImageBytes = await fetch(jpgUrl).then((res) => res.arrayBuffer());
  const jpgImage = await pdfDoc.embedJpg(jpgImageBytes);
  const jpgDims = jpgImage.scale(0.25);
  // Get the width and height of the first page
  const { width, height } = firstPage.getSize();
    firstPage.drawText('This text was added with JavaScript!', {
       x: 5,
       y: height / 2 + 300,
       size: 50,
       font: helveticaFont,
       color: rgb(0.95, 0.1, 0.1),
       rotate: degrees(-45),
        // Add a blank page to the document
 firstPage.drawImage(jpgImage, {
    x: firstPage.getWidth() / 2 - jpgDims.width / 2,
    y: firstPage.getHeight() / 2 - jpgDims.height / 2,
    width: jpgDims.width,
    height: jpgDims.height,
  // Serialize the PDFDocument to bytes (a Uint8Array)
  const pdfBytes = await pdfDoc.save();
        // Trigger the browser to download the PDF document
  download(pdfBytes, "pdf-lib_modification_example.pdf", "application/pdf");
        
Thanks for contributing an answer to Stack Overflow!
Please be sure to answer the question. Provide details and share your research!
But avoid …
Asking for help, clarification, or responding to other answers.
Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.