Compress PDF
Shrink large PDFs down for easy sharing — free and private.
Also known as: PDF compressor, PDF size reducer, PDF shrinker, PDF optimizer
How it works
- 1Upload the PDF you want to compress.
- 2Choose a compression level: High quality (larger file), Balanced, or Small size (maximum compression).
- 3Click "Compress PDF" and wait for processing to finish.
- 4Download your compressed file and compare the new size against the original.
Why use Compress PDF
Three quality presets
Pick High quality, Balanced, or Small size depending on whether fidelity or file size matters more.
Great for scans
Image-heavy and scanned PDFs typically see the largest size reductions — often 50–90%.
See the size difference
Compare the original and compressed file sizes right on the page before downloading.
Nothing uploaded
Rendering and re-encoding both happen locally in your browser — your file never reaches a server.
No account, no watermark
Compress as many files as you want, with no signup and no branding added to your output.
Fast, even on large files
Processing runs directly on your device's hardware, without waiting on an upload or a server queue.
Who uses Compress PDF
Email attachment limits
Shrink a large scanned document so it fits under your email provider's attachment size cap.
Portal upload limits
Reduce file size to fit under a job application, government, or school portal's upload limit.
Faster sharing
Compress a photo-heavy PDF report before sending it over a slow connection.
Saving storage space
Shrink a folder of scanned documents to save space on a phone or cloud storage plan.
Web-friendly PDFs
Compress a PDF that will be downloaded from a website, so visitors get a faster download.
Archiving scans
Bring large batch-scanned documents down to a manageable size before long-term archiving.
About Compress PDF
A PDF can balloon in size for a lot of reasons — high-resolution scans, embedded photos, or a document that was exported with unnecessarily large images baked in. Compress PDF exists to bring that file size back down so it's easier to email, upload to a portal with a size limit, or store without eating up disk space.
The way this tool compresses a PDF is by rendering each page with pdf.js (the same rendering engine behind Chrome's built-in PDF viewer) and then re-encoding that rendered page as an optimized image at the quality level you choose, before rebuilding the document with pdf-lib. This approach — similar to how most online PDF compressors handle scanned or image-heavy files — is very effective at shrinking file size, especially for scans and photo-heavy documents, but it does mean each page becomes a flattened image rather than a page of live, selectable text.
All of this happens locally in your browser tab. The original file is read from your device, rendered and re-encoded on your device, and the compressed output is handed straight back to you — no upload, no server-side processing queue, no third party holding a copy of your document while it's compressed.
If you need to keep text selectable and searchable after compression — for example, a text-heavy contract you'll need to search later — this tool's image-based approach isn't the right fit; it's best suited to scans, image-heavy PDFs, and documents where visual fidelity matters more than selectable text.
Compress PDF vs. other options
How Open Tools Library compares to desktop software and other online tools.
| Feature | Open Tools Library | Desktop software | Other online tools |
|---|---|---|---|
| Price | Free, unlimited | Often paid or subscription | Often free with daily limits |
| Installation | None | Required | None |
| File privacy | Never leaves your device | Stays local | Uploaded to a server |
| Quality control | 3 presets | Usually adjustable | Varies, often fixed |
| Speed | Instant, on-device | Fast | Depends on upload speed |
| Watermarks | Never | Never | Sometimes on free tiers |
Pro tips
- Start with "Balanced" — it usually gives the best trade-off between size and visual quality.
- If the file is still too large, try "Small size", especially for scanned or photo-heavy PDFs.
- Remember that compression flattens each page into an image — don't compress a document if you need to keep the text selectable or searchable.
- Compress after merging, not before — merge first, then compress the combined file once.
- Compare the before/after size shown on the page to decide if the quality trade-off is worth it for your use case.
Technical specs
- Compression levels
- High quality, Balanced, Small size
- Supported input
- Output format
- .pdf (image-based pages)
- Text selectability
- Not preserved — pages become images
- Typical size reduction
- 50–90% on scanned/image-heavy PDFs
- Processing location
- 100% local, in your browser
Privacy & security
Compression is often the last step before sending a file somewhere — email, a portal, a client — so it's worth knowing exactly where that processing happens.
Rendering and re-encoding both happen locally; your original PDF never leaves your device.
No account or signup — compress a confidential scan the same way you'd compress a flyer.
The compressed file exists only where you save it — nothing lingers on a server afterward.
Works the same whether you're shrinking a signed contract or a batch of vacation photos.
Frequently asked questions
Will compressing affect text selection?
Yes. This tool rasterizes each page into an optimized image to achieve strong size reduction, similar to how many online compressors handle scanned or image-heavy PDFs. Selectable text becomes a flattened image after compression.
How much smaller will my file be?
It depends on the original content. Image-heavy and scanned PDFs typically shrink the most — often 50–90%.
Is this tool private?
Yes, compression runs entirely in your browser. Files are never uploaded to a server.
Which compression level should I choose?
"Balanced" is a good default. Choose "High quality" if visual fidelity matters most, or "Small size" when you need the smallest possible file.
Can I compress a PDF more than once?
Yes, but repeated compression compounds quality loss since each pass re-encodes the images again. It's best to compress once from the original file.
Is there a limit to how many PDFs I can compress?
No. Compress as many files as you like, for free, with no account required.
Troubleshooting
My compressed PDF is bigger than I expected
Text-heavy PDFs with few images compress less dramatically than scans, since there's less redundant image data to optimize. Try the "Small size" preset for a stronger reduction.
The text isn't selectable anymore
This is expected — compression re-renders each page as an optimized image, similar to how most online PDF compressors handle image-heavy files. If you need selectable text, keep a copy of the original alongside the compressed version.
Compression is taking a while
Very large or high page-count PDFs take longer since every page is rendered and re-encoded on your device. Processing time depends on your device's hardware, not on network speed.
The output looks blurry
Try a higher quality preset — "Small size" prioritizes file size over visual fidelity. "High quality" or "Balanced" will look sharper.
Related searches
Landed here looking for something worded a little differently? Compress PDF covers all of these too:
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