Compress PDF online for free
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Your files never leave your browser
Large PDF files are a common problem when uploading documents to government portals, email attachments, or online application forms that cap file size. This tool re-saves your PDF with optimised internal structure directly in your browser, so nothing ever leaves your device. It works well for text-heavy PDFs like reports, forms, and invoices. If your PDF is a scanned document or full of large photos, browser-only compression has a lower ceiling than server-side image recompression — for those files, expect a modest size reduction here rather than a dramatic one.
Why some PDFs shrink a lot and others barely move
It comes down to what is actually taking up space inside the file. A PDF exported from Word, Excel, or an accounting system stores text as text — characters plus font references — which is extremely compact, and most of the remaining size is structural overhead that optimisation can strip out. A scanned PDF is the opposite: every page is a photograph of paper, and that image data is already compressed by the scanner. Browser-based optimisation can tidy the PDF's internal structure, but it cannot re-encode those page images, which is why a 12MB scan often stays close to 12MB while a 4MB report drops sharply.
The fix for scanned PDFs is upstream, not downstream
If your file is a scan, the most effective change happens before compression: rescan at 200 DPI instead of 600, and choose greyscale or black-and-white instead of colour if the original is dark text on white paper. Those two settings routinely cut file size by five to ten times while leaving the text perfectly readable, because you are removing data that was never carrying information in the first place. Scanning a text document in full colour at 600 DPI stores the subtle paper texture and yellowing in fine detail — none of which anyone needs.
When to stop compressing
There is a point where further compression costs you more than it saves. If a portal accepts 500KB and your file is 480KB, you are done — pushing to 200KB only risks legibility for no benefit. Check the actual limit before optimising for a number you assumed. It is also worth opening the compressed file and reading the smallest text on the page before you submit it; a document that technically uploads but cannot be read by a verifying officer is worse than one that was slightly too large.
Frequently asked questions
- Is this PDF compressor really free?
- Yes. Compression happens entirely in your browser, so there's no server cost to us and no signup wall for you.
- Does compressing reduce PDF quality?
- Text and vector content stay identical. Any embedded images are not re-encoded by this client-side tool, so visual quality is preserved — the size reduction comes from optimising the PDF's internal structure.
- Will my file be uploaded anywhere?
- No. Processing happens locally in your browser using JavaScript. Your file never leaves your device.
- Why didn't my scanned PDF get much smaller?
- Scanned PDFs are mostly large embedded images, and browser-side tools can't safely re-encode those without a server. If you need a scanned PDF down to an exact target size, look for a server-based compressor instead.
- What's the maximum file size I can compress?
- Since everything runs in your browser's memory, very large files (500MB+) may be slow or fail depending on your device's available RAM.
- Is there a file size limit?
- There is no server-side limit because nothing is uploaded, but very large files (roughly 500MB and up) depend on your device's available memory and may be slow or fail on a phone.
- Why is my compressed file the same size or slightly larger?
- Some PDFs are already optimally stored, and re-saving them adds no benefit. If the output is not smaller, keep your original — the tool has simply found nothing left to remove.