How to compress a PDF and reduce its file size
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 fileentirely 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.