How to Compress a PDF
Need to shrink a PDF that is too large to email or upload? Here's how to compress a PDF online for free — no uploads, no software, no sign-up.
Why are PDFs so large?
PDFs grow large because of high-resolution images, embedded fonts, multiple layers, and uncompressed data streams. A scanned document at 600 DPI can easily reach 50–100 MB. Compression reorganizes these elements to take up less space without visible quality loss.
How to compress a PDF online (free)
Go to the Compress PDF tool. Upload your PDF. Click 'Compress PDF' — the processing happens entirely in your browser. The tool shows the original size, the new size, and the compression ratio. Download the compressed file.
What compression method does this use?
This tool uses pdf-lib's built-in optimization, which re-encodes PDF streams and consolidates objects. This typically reduces file size by 10–30% with no quality loss. For maximum compression (50%+ reductions) on scanned PDFs, advanced tools use Ghostscript WASM, which we're evaluating for a future update.
Will compression reduce quality?
Minimal quality loss. pdf-lib re-encodes streams but doesn't recompress embedded images aggressively. For most documents, the output looks identical to the original. For image-heavy scanned PDFs, visible quality changes are minimal at default settings.
What if my file is already small?
Compression may make already-optimized files slightly larger because of object stream overhead. If the tool shows a 0% or negative reduction, the file is already compressed as much as this method can do.
Is compression safe?
Yes. The tool runs entirely in your browser. Your file never leaves your device. No uploads, no servers, no logs.
Frequently Asked Questions
What's the maximum file size?
There's no hard limit. Your browser loads the file into memory, so the practical limit depends on your device. For most computers, files up to 200 MB work comfortably.
Can I compress a scanned PDF?
Yes, but the reduction will be smaller than for text-based PDFs. Scanned PDFs are mostly image data, which this tool's optimization handles less aggressively.
Can I compress multiple PDFs at once?
Not yet — one at a time. Compress each file individually, then merge them back together using the Merge PDF tool.