A PDF that's too big to email or too slow to upload is a daily annoyance. Compressing a PDF reduces its file size so it's easier to share, and you can do it for free without uploading your document to a stranger's server.
Why are PDFs so big in the first place?
Almost always, it's images. A PDF full of high-resolution scans or photos carries a lot of pixel data. Plain-text PDFs are already tiny, which is why compressing them barely helps. Compression works by re-encoding those embedded images at a smaller size, cutting the bulk while keeping the page readable.
How to compress a PDF (step by step)
- Open the Compress PDF tool and upload your file.
- Choose a level: Light (best quality), Recommended (balanced), or Strong (smallest file).
- Click Compress PDF. The tool shows your before-and-after size and how much you saved.
- Download the smaller version.
How small can it get?
It depends entirely on the content. Scanned and photo-heavy PDFs can often drop 40-70%. A text-only PDF may not shrink at all, and that's fine, because it was already small. If the tool says your file is "already well optimized," that's a good sign, not a failure.
When to compress
- Email limits, most inboxes cap attachments around 20-25 MB.
- Web uploads, job portals and forms often have strict size caps.
- Storage & sharing, smaller files sync and download faster.
Tips for quality
- Compress last. Do your merging, splitting and organizing first, then compress the final file.
- Keep an original. Compression is lossy for images, hang on to the full-quality version.
- Very large scans? Consider scanning at 200-300 DPI rather than 600 DPI next time.
🗜️ Ready to compress pdf?
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Open the Compress PDF tool →Frequently asked questions
How do I reduce PDF file size for free?
Upload your PDF, choose a compression level and click Compress PDF. PDFOtter shrinks it and shows the new size, free and private.
Which compression level should I choose?
Start with "Recommended" for a good balance. Use "Strong" for the smallest file, or "Light" to preserve maximum quality.
Why did my PDF not get smaller?
PDFs that are mostly plain text are already tiny. Compression helps most on scanned or image-heavy documents.
Is my file uploaded to compress it?
No. Compression happens on your device, so your document is never sent anywhere.