Building a Privacy-First PDF Toolkit That Runs Entirely in Your Browser

xinping cheng — Tue, 31 Mar 2026 04:09:06 +0000

The Problem
Ever needed to merge a few PDFs or compress a large file, only to find yourself uploading sensitive documents to some random website? I've been there too many times.
Most online PDF tools:
Upload your files to their servers
Have unclear privacy policies
Are bloated with ads and upsells
Require registration for basic features
I wanted something better: a tool that's fast, free, and respects your privacy.
The Solution
I built PDF Tools Online - a completely client-side PDF processor. Your files never leave your device.
Core Features
📄 PDF Merge - Combine multiple PDFs into one document
✂️ PDF Split - Extract specific pages or split into separate files
📉 PDF Compress - Reduce file size without significant quality loss
🖼️ PDF to Image - Convert PDF pages to PNG/JPG
📷 Image to PDF - Create PDFs from multiple images
Tech Stack
The app is built with:
React - For the UI
pdf-lib - Client-side PDF manipulation
Tailwind CSS - Styling
Vite - Build tool
Why Client-Side Processing?
Processing files in the browser has several advantages:
Privacy - Your files never leave your device. No server uploads, no data retention.
Speed - No network latency. Processing happens instantly on your machine.
Cost - No server infrastructure needed. The app is just static files.
Offline-capable - Once loaded, it works without internet (with proper PWA setup).
Key Implementation Details
PDF Merging

import { PDFDocument } from 'pdf-lib';

async function mergePDFs(pdfFiles) {
  const mergedPdf = await PDFDocument.create();

  for (const file of pdfFiles) {
    const pdfBytes = await file.arrayBuffer();
    const pdf = await PDFDocument.load(pdfBytes);
    const copiedPages = await mergedPdf.copyPages(pdf, pdf.getPageIndices());
    copiedPages.forEach((page) => mergedPdf.addPage(page));
  }

  return await mergedPdf.save();
}

PDF Compression

async function compressPDF(file) {
  const pdfBytes = await file.arrayBuffer();
  const pdfDoc = await PDFDocument.load(pdfBytes);

  // Remove metadata and optimize
  pdfDoc.setTitle('');
  pdfDoc.setAuthor('');
  pdfDoc.setSubject('');
  pdfDoc.setKeywords([]);
  pdfDoc.setProducer('');
  pdfDoc.setCreator('');

  return await pdfDoc.save({ useObjectStreams: false });
}

PDF to Image

import * as pdfjsLib from 'pdfjs-dist';

async function pdfToImages(file) {
  const arrayBuffer = await file.arrayBuffer();
  const pdf = await pdfjsLib.getDocument({ data: arrayBuffer }).promise;
  const images = [];

  for (let i = 1; i <= pdf.numPages; i++) {
    const page = await pdf.getPage(i);
    const viewport = page.getViewport({ scale: 2 });
    const canvas = document.createElement('canvas');
    const context = canvas.getContext('2d');

    canvas.width = viewport.width;
    canvas.height = viewport.height;

    await page.render({ canvasContext: context, viewport }).promise;
    images.push(canvas.toDataURL('image/png'));
  }

  return images;
}

Challenges & Solutions
Challenge 1: Large File Handling
Browser memory limits can cause crashes with large PDFs. Solution: Process files in chunks and use Web Workers for heavy operations.
Challenge 2: Browser Compatibility
Different browsers handle file APIs differently. Solution: Feature detection and polyfills for older browsers.
Challenge 3: User Experience
Users need visual feedback during processing. Solution: Progress indicators and drag-and-drop file upload.
What's Next?
Future features I'm considering:
PDF editing (add text, annotations)
OCR for scanned documents
Batch processing
PWA support for offline use
PDF form filling
Try It Out
Check it out at pdftoolsonlineapp.com
The project is open to feedback! What PDF features would you find most useful?
Conclusion

Building a privacy-first tool taught me that client-side processing is not just about privacy - it's about speed, cost-efficiency, and user trust. With modern browser APIs and libraries like pdf-lib, we can build powerful tools without compromising user data.

What are your thoughts on client-side vs server-side processing for file manipulation tools? Drop a comment below!

DEV Community: xinping cheng

Building a Privacy-First PDF Toolkit That Runs Entirely in Your Browser

Building a privacy-first tool taught me that client-side processing is not just about privacy - it's about speed, cost-efficiency, and user trust. With modern browser APIs and libraries like pdf-lib, we can build powerful tools without compromising user data.