100% Private & Secure — Files Never Leave Your Device
Compress PDF files without uploading them
Reduce PDF size by up to 90% right inside your browser. No server, no sign-up, no watermark — and it keeps working with your internet switched off.
Why compress in the browser?
Files never leave your device
Compression runs in WebAssembly inside your browser. There is no upload step, so there is nothing to intercept, log or retain.
No upload wait
Server-based tools spend most of their time transferring your file. Here processing begins the instant you drop it in.
Exact target size
Need to be under 100 KB? Type it in. We step through quality levels and stop at the best one that still fits.
Genuinely unlimited
No daily quota, no file-count cap, no watermark and no premium tier. Your CPU does the work, so metering makes no sense.
Works offline
Load this page once, then disconnect entirely. The compressor keeps working because it is already running locally.
Safe for sensitive documents
Contracts, medical records, passport scans and financial statements stay on your machine from start to finish.
How to compress a PDF
- 1
Drag your PDF files into the drop zone, or click to browse. Multiple files are supported.
- 2
Pick a compression level, or switch to Target Size and type the exact size you need.
- 3
Press Compress. Everything runs on your own device, with a live progress bar per file.
- 4
Download your optimized PDFs individually, or grab them all at once.
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Frequently Asked Questions
Are my files uploaded to a server?
No. Compression runs entirely inside your browser using WebAssembly. Your PDF is read into local memory, processed on your own CPU and written straight back to your downloads folder. No network request ever carries the file.
Is this PDF compressor really free?
Yes, with no file limits, no watermarks and no account. Because processing happens on your device rather than our servers, there is no per-file cost to recover and therefore no reason to meter your usage.
How much smaller will my PDF get?
It depends on the content. Scanned or image-heavy documents commonly shrink by 70–95%. Text-only PDFs that were already optimized may only drop 5–20%, since there is little redundant data left to remove.
Does compression reduce the quality of my PDF?
Text always stays sharp because it remains real vector text rather than an image. Embedded photographs are downsampled and re-encoded, so quality loss scales with how aggressive a preset you choose. Less Compression is visually near-identical to the original.
Can I compress multiple PDFs at once?
Yes. Drop in as many files as you like — they are queued and processed one after another so memory stays under control. Each file gets its own progress bar and download button, plus there is a Download All option.
Which browsers are supported?
Any modern browser with WebAssembly support: Chrome, Edge, Firefox, Safari, Brave, Opera and Arc, on desktop and mobile. Chromium-based desktop browsers are typically the fastest for very large documents.
Can I compress a password-protected PDF?
Not directly. Encrypted PDFs must have their password removed first, which you can do in Acrobat, Preview on macOS, or by opening the file and re-printing it to PDF with the password supplied. Then compress the unprotected copy here.
Does this work on mobile phones and tablets?
Yes. The interface is fully responsive and the engine runs on iOS and Android. Bear in mind that mobile devices have less memory, so very large files (over roughly 50 MB) may be slow or fail on older phones.
What happens to my file after compression?
Nothing persists. The compressed result lives in your browser tab's memory until you download it, and everything is discarded the moment you close or refresh the page. There is no server-side copy because the file was never sent anywhere.
Why did my file barely get smaller?
Your PDF was probably already optimized — for instance exported by Acrobat with compression enabled, or generated as pure text with subset fonts. When we cannot beat the original we deliberately return your untouched file rather than a worse one.
How CompressPDF compresses your PDF
PDF files grow large for predictable reasons. Scanners embed full-colour page photographs at 300 or 600 DPI. Word and InDesign exports carry entire font families when a subset of a few dozen glyphs would do. Incremental saves leave behind orphaned objects from every previous revision, and form definitions, XMP metadata blocks and duplicate image resources accumulate silently.
Our engine attacks all of these. A structural pass garbage-collects unreferenced objects, deduplicates identical images, subsets fonts down to the glyphs actually used and repacks the remaining objects into compressed object streams. An image pass then downsamples embedded raster content to a resolution appropriate for your chosen preset and re-encodes it through an optimized JPEG pipeline. Text stays as real vector text throughout, which is why it remains sharp at any compression level.
All of this executes as WebAssembly — the same technology behind Figma and Photoshop on the web — running on your own processor inside a Web Worker, so the interface never freezes. The practical consequence is architectural rather than a promise: because no network request ever carries your document, there is no server that could store, log or leak it.