Compress PDF Without Losing Quality
Reduce the file size of your PDFs for easy sending. Premium and 100% local optimization, ideal for law firms and clinics.
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Compress your PDF files locally, quickly and securely
Our tool allows you to drastically reduce the file size of your PDFs in seconds. Ideal for sending heavy documents via email. No registration required and everything is processed on your device.
Almost every article about compressing a PDF is vague about what compression actually does, which is why people are so often disappointed by the result. There are two entirely different operations hiding behind the word, and knowing which one you need is the difference between a file that shrinks and a file that does not.
The first is structural optimisation. A PDF accumulates cruft: objects that nothing references any more, duplicated font descriptors, a cross-reference table bloated by successive incremental saves. Optimising strips all of that and rewrites the file compactly. It is completely lossless — your text stays selectable text and your images keep every pixel — but it can only reclaim waste that is actually there.
The second is rasterisation, offered here as the aggressive mode. Each page is rendered to an image and the PDF is rebuilt from those images. This shrinks files dramatically and unconditionally, because it replaces whatever was there with a JPEG. The cost is real: text becomes pixels, and it is no longer selectable, searchable or sharp when zoomed.
Total Privacy When Compressing
Your documents are never uploaded to the cloud. Compress contracts, receipts, or files with peace of mind directly in your browser.
Smart Compression
We reduce the file size while maintaining the maximum visual quality possible. Perfect for meeting attachment limits.
Optimization on Any Device
Compress your PDFs from your desktop PC, MacBook, or smartphone with the same advanced performance.
How to compress a PDF
Select your PDF file or drag it to the upload area.
Wait for our tool to analyze and reduce the file size.
Compare the original size with the compressed size.
Download your optimized PDF file, ready to share.
Guaranteed Confidentiality When Compressing PDFs
By using ZasPDF to reduce your document sizes, you avoid the risks of sending confidential files to third-party servers. The compression process happens natively in your device's RAM, ensuring your private information stays private.
When people reach for this
Getting under an email attachment limit
Most mail servers reject attachments over 20 to 25 MB. A scanned contract or an image-heavy report routinely exceeds that, and compression is usually quicker than setting up a file transfer.
Uploading to a portal with a hard cap
Tax authorities, court filing systems and job application portals impose limits that are frequently lower than email — sometimes 5 MB. The aggressive mode exists mainly for these.
Archiving years of scanned documents
Scans are stored as full-resolution images and dominate any document archive. Compressing them makes the difference between an archive that fits on a drive and one that does not.
Publishing a document for download
A 40 MB PDF on a slow connection is a document nobody reads. Reducing it respects the reader's bandwidth and time.
What actually happens to your file
There are three levels here, and it matters which one is selected, because two of the three rasterise the page and one does not. "Basic" is the only lossless option: the document is passed to pdfcpu's optimiser, compiled to WebAssembly, which walks the object graph and removes what the document no longer needs — orphaned objects, duplicate resources, the accumulated layers of a cross-reference table that has been appended to repeatedly. It does not touch content streams, so images are not re-encoded and text is not re-rendered.
"Recommended" and "Extreme" both take a different route: each page is rendered to an offscreen canvas by pdf.js and re-embedded as a JPEG. They differ only in how aggressively — Recommended renders at full scale and JPEG quality 0.4, Extreme at half scale and quality 0.2 — but both replace your vector content with a picture of it. "Recommended" is the level selected by default.
We tested this ourselves rather than describing it in the abstract. On a 40-page text report (83 KB), Basic reduced it to 73 KB — a genuine 12% saved with the text still selectable. Recommended, the default, turned that same file into 4.16 MB: fifty times larger, because rendering vector text as a full-resolution JPEG is a spectacularly inefficient way to store it. Extreme produced 599 KB — still seven times the original, and now with the text unreadable and unselectable.
On an 8-page scanned document (32.2 MB of high-resolution photographs), the pattern flips entirely. Basic barely moved it, 33.72 MB, because there is no structural waste to remove from an image-heavy file. Recommended brought it to 291 KB and Extreme to 86 KB — reductions of 99.1% and 99.7% — because that is exactly the case rasterisation and re-compression are good at.
The conclusion follows directly from the mechanism: whether "Recommended" helps or actively hurts depends entirely on what is already on the page. For a scanned or image-heavy document it is transformative. For a text-based one, it is the worst option on offer, and the fact that it is pre-selected is worth knowing before you click Compress.
Where it falls short, honestly
- "Recommended" can make a text-based file dramatically larger, not smaller — our own test turned an 83 KB report into 4.16 MB. If your document is mostly text, use "Basic" instead, whatever the label on the other option suggests.
- "Basic" may barely change the size, and that is the expected outcome for a well-formed file. A PDF exported cleanly from modern software has little redundancy to reclaim. Nothing is wrong — there was simply nothing to remove.
- "Basic" does not downsample images. If your file is 30 MB because it contains twenty 300 DPI scans, it will not meaningfully help; the image data is genuinely being used.
- Both "Recommended" and "Extreme" destroy the text layer. The output cannot be searched, copied from, or converted to Word afterwards. Keep the original.
- "Extreme" is visibly lossy — fine print, thin lines and detailed graphics show artefacts at quality 0.2. Always look at the result before sending it to anyone.
- Rendering every page to a canvas is memory-hungry. Very long documents processed with "Recommended" or "Extreme" are the most likely to exhaust the tab.
- Already-compressed files do not compress again. A file produced by this tool, or by any optimiser, has little left to give.
Compared with an online compressor
| This tool | Typical cloud compressor | |
|---|---|---|
| Where your file goes | Nowhere. It stays in the browser tab. | Uploaded to a server you do not control. |
| What it does to your file | Documented above, both modes. | Rarely disclosed; often silent rasterisation. |
| Lossless option | Yes — standard mode never re-encodes. | Sometimes, sometimes not, hard to tell. |
| File size limits | Bounded only by your device's memory. | Commonly capped on free tiers. |
| Works offline | Yes, once the page has loaded. | No. |
| Watermarks | None. | Frequently added on free tiers. |