How to compress a PDF and reduce its file size (free)
Last updated: June 25, 2026
"The attachment is too large." If you've seen that message, you've met the most common PDF problem there is. Scanned documents and image-heavy reports balloon to 10, 20, even 50 MB — well over the limits most email providers and upload forms allow. Compressing the PDF fixes it, and you can do it for free.
Compress a PDF in your browser
- Open the Compress PDF tool.
- Choose your PDF file.
- Pick a level: Recommended is the best balance for most files; Strong squeezes the hardest; Light keeps the most detail.
- Press Compress PDF. The smaller file downloads automatically, and you'll see exactly how much space you saved.
Why some PDFs shrink a lot — and others don't
Most of a large PDF's weight comes from images: scans, photos, screenshots. Compression re-encodes those images at a sensible resolution and quality, which can cut the size by 70–90% on a scanned document. A PDF that is purely text, on the other hand, is usually already small, so there's little to gain — and robinpdf will simply tell you if it can't make a file meaningfully smaller instead of handing you a worse copy.
Choosing the right level
- Emailing a scan? Recommended or Strong is usually invisible to the eye and gets you well under typical 10 MB and 25 MB limits.
- Printing later? Use Light to preserve more detail.
- Just need it to fit a form? Try Recommended first, then Strong if it's still too big.
Private by design
Many "compress PDF" sites upload your document to their servers. robinpdf compresses the file entirely on your device — nothing is sent anywhere, which matters when the PDF is an invoice, a contract or an ID scan.
Frequently asked questions
Will the text still be readable?
Yes. At Recommended level, pages stay crisp on screen and in normal printing.
Is there a file-size limit?
No artificial limit — the work happens locally, so the limit is your device's memory.
Does it work for scanned documents?
Especially well — scans are mostly images, which is exactly what compression targets.