Browser-only PDF jobs with pdf-lib: 4x6 label crop that keeps barcodes vector, real redaction, 2-up card sheets

[emma-walton]

Hi! I make fbuff.com, a set of free tools that run entirely in the browser, and pdf-lib does the PDF writing for most of them. Sharing three patterns that worked well, in case they help someone.

1. Crop a shipping label to 4x6 and keep the barcode vector

Carriers hand out a Letter page with the label in one corner. Instead of rasterizing, embedPage takes a bounding box, so only the label is copied and the barcode stays sharp at any printer resolution:

const out = await PDFDocument.create();
const original = await PDFDocument.load(bytes, { ignoreEncryption: true });
const from = original.getPage(0);
const view = from.getCropBox();
const embedded = await out.embedPage(from, {
  left: view.x + rect.x,
  bottom: view.y + rect.y,
  right: view.x + rect.x + rect.width,
  top: view.y + rect.y + rect.height,
});
out.addPage([288, 432]).drawPage(embedded, { x, y, width, height, rotate: degrees(turn) });

Remember to add the crop box origin (view.x, view.y): some carrier PDFs don't start at 0,0. Pages that have their own /Rotate were easier to handle as a 300 DPI raster fallback.

2. Redaction that really removes the text

Drawing black rectangles over a PDF leaves the text underneath selectable. The redactor renders each page with PDF.js at 200 DPI, burns the boxes into the canvas, and builds a new document from the JPEGs, with PDFDocument.create({ updateMetadata: false }) so no producer, creator or dates are written and nothing is copied from the original file.

3. Two 4x6 cards on one Letter sheet

For printable cards, one embedPng and two drawImage calls on a landscape 792x612 page, plus short drawLine crop marks just outside each corner so the cut follows the card edge without printing on it.

pdf-lib is loaded with a dynamic import("pdf-lib") only when the user clicks download, which keeps it out of the first page load.

The tools, if you want to see them in action: Shipping Label to 4x6, PDF Redactor, Save the Date Maker. Thanks for the library, it made all of this possible without a server.