Online PDF Compressor
Compress PDF files online for free. Reduce size, maintain quality. Secure local processing.
How to Use
Select file
Start process
Local processing
Download result
Complete PDF Compression Guide
How Compression Works
Allin PDF compresses files entirely in your browser (pdf-lib plus the browser's own image re-encoding, running in a Web Worker), so nothing is uploaded to a server. There are three levels: 1) Low — lossless: uses object streams and removes unreferenced objects, images untouched; 2) Medium (default) — downscales embedded images to 2000 px on the longest side and re-encodes them as JPEG at quality 0.72; 3) High — 1400 px longest side, JPEG quality 0.55, and document metadata is removed. If the result is still at least 98% of the original size, you get the original file back. How much smaller the file gets depends on how many images the PDF contains and their resolution.
Balancing Quality vs File Size
The key consideration when compressing PDFs is: how small do you need the file, and how much quality loss is acceptable? Pick Low for lossless cleanup, the default Medium for everyday use, and High when you need the smallest file (for example, strict upload limits). For text-heavy documents (contracts, papers), compression mainly affects images and redundant data, so the text itself is unchanged. For image-heavy documents (brochures, PPT-to-PDF), Medium and High lower image resolution, but pages usually stay clear for on-screen reading. If you need to email an attachment (often limited to 25MB) or meet an upload limit, try Medium first and switch to High if it is not small enough.
Processing Results
Technical Specifications
Feature Comparison
| Feature | Allin PDF | Other Tools |
|---|---|---|
| File privacy | Processed in your browser, no upload | Many online tools upload files to their servers |
| Compression levels | Low (lossless) / Medium / High | Varies by tool |
| Batch and usage | Up to 20 files, unlimited runs | Varies by service and plan |
Key Facts
Allin PDF offers three compression levels: Low is lossless (object streams plus removal of unreferenced objects); Medium (default) caps images at 2000 px on the long edge with JPEG quality 0.72; High caps them at 1400 px, quality 0.55, and strips metadata.
Allin PDF compresses PDFs in your browser with pdf-lib in a Web Worker, so files are never uploaded and no sign-up is needed.
Allin PDF compresses up to 20 PDFs per batch with no usage cap; files can be up to 5 MB on the free plan and 50 MB on Pro.
If the compressed file would still be at least 98% of the original size, Allin PDF returns the original file instead of a bigger or barely smaller one.
Privacy Protection
This tool processes your files in your browser: they are not uploaded to a server, and no sign-up or login is needed.
Related Articles
FAQ
How much can a PDF be compressed without losing quality?
It depends on the content, so there is no fixed percentage. Low is lossless (object streams and cleanup of unreferenced objects, images untouched). Medium (default) downscales images to 2000 px on the longest side at JPEG quality 0.72; High uses 1400 px at quality 0.55 and also removes metadata. Image-heavy PDFs shrink the most; text-only PDFs change little. If the result is not smaller than 98% of the original, you get the original back.
Is PDF compression done locally or in the cloud?
Completely local. Allin PDF compresses PDFs entirely in your browser (pdf-lib and browser image re-encoding in a Web Worker). Your file never leaves your device and is never uploaded to any server, and processing speed does not depend on your upload speed.
Can I compress a PDF without registration or login?
Yes. PDF compression on Allin PDF is completely free with no registration, no login, no daily limits, and no watermarks added. Just drag and drop your file to compress instantly.
What do the Low, Medium and High compression levels do?
Low is lossless: it restructures the PDF with object streams and removes unreferenced objects without touching images. Medium (the default) downscales images to 2000 px on the longest side and re-encodes them as JPEG at quality 0.72. High uses 1400 px and quality 0.55, and also removes document metadata.
Process Documents Anywhere
Download the Allin PDF iOS app. Its local tools also work offline.