Reduce file size while preserving quality. Re-renders pages at your chosen DPI & quality — your file never leaves this device.
PDFZero shrinks PDF file size directly inside your browser — there's no upload to a server, no signup, and no watermark added to your file. Pick a PDF, choose a compression level, and download the smaller version in seconds. Because the whole process runs on your device using PDF.js and pdf-lib, your document never leaves your computer, which makes this approach to PDF compression more private than tools that require you to upload files to the cloud.
Large PDFs are slow to email, can exceed attachment size limits, and take longer to upload to portals or forms. Compressing a PDF reduces its size — often by 50–90% — by lowering the resolution of embedded images while keeping the document fully readable. This is especially useful for scanned documents, PDFs with photos, or presentation exports that are much larger than they need to be.
When you use a traditional online PDF compressor, your file is uploaded to a remote server, processed there, and sent back to you — which means a copy of your document leaves your device and sits on someone else's infrastructure, at least temporarily. PDFZero works differently. The moment you select a file, it is loaded straight into your browser's memory and rendered with PDF.js; each page is then re-encoded at your chosen resolution and rebuilt into a new PDF with pdf-lib, all using your browser's own WebAssembly engine and Web Workers. No part of the file is ever transmitted over the network. This is what makes PDFZero a genuinely private PDF compressor rather than a cloud service with a privacy promise attached.
Uploading a PDF to a server creates several risks that a client-side tool simply does not have: the file can be logged, cached, retained after processing, or exposed if the server is breached, and you have to trust the provider's data-handling policy. Because PDFZero performs in-browser PDF compression entirely on your own machine, there is no upload, no server-side copy, and nothing to retain or leak — the document never crosses the network. That also means the tool keeps working on flaky connections and behaves like a true offline PDF tool once the page has loaded. For contracts, IDs, medical records, financial statements, and any confidential document, processing locally is the most private option available.
Yes. PDFZero is a private PDF compressor that runs entirely in your browser using PDF.js and pdf-lib. After the page loads, compression happens offline on your own device, and your file is never uploaded to any server — so it works without an internet connection and keeps confidential documents completely local.
Yes. PDFZero compresses the file using your browser's own processing power (WebAssembly and Web Workers). The PDF is never uploaded to any server, so sensitive or confidential documents stay on your device the entire time.
It depends on the content. PDFs made mostly of scanned images or high-resolution photos can often shrink by 70–90% using the Screen or Balanced modes. PDFs that are mostly text see smaller reductions since text doesn't compress the same way as images.
Compression re-renders each page as an image at a lower DPI and quality setting, so there is some quality tradeoff. The Balanced and High quality modes are designed to keep text and images clearly readable. Use High quality mode if you plan to print the document.
No. Because compression happens locally in your browser instead of being uploaded to a server, there's no server-side file size cap. Very large files may simply take longer to process depending on your device's performance.
No. PDFZero's compress tool is free to use with no signup required and no watermark added to your downloaded file.