Compress PDF
Shrink large PDFs to a fraction of their size with three compression levels. The compression engine runs entirely on your own device.
- No uploads
- Runs locally
- No sign-up
Your files are processed locally in your browser — nothing is uploaded.
How to compress a PDF
- Add the PDF you want to shrink by dragging it onto the upload area, or click to browse (up to 150 MB).
- Pick a compression level: Extreme for the smallest size, Recommended for a balance, or Light for print quality.
- Click "Compress PDF". The first run downloads the compression engine once; afterwards it starts instantly.
- Download the compressed PDF and compare the sizes — the original file stays untouched on your device.
Compress large documents without uploading them
A PDF that needs compressing is usually one that is about to be sent somewhere — a scanned contract going to a lawyer, a portfolio going to a recruiter, medical reports going to an insurer. Ironically, most online compressors make you upload the file to their servers first, so shrinking a sensitive document starts with giving it away. CoolPDF compresses the document where it already is: inside your browser, on your own device. The compression engine — the same Ghostscript trusted by print shops for decades — is compiled to WebAssembly and downloaded to your machine once. Your file is read from your disk, rebuilt smaller, and saved back to it, with no upload, queue, or remote copy at any point. Close the tab and nothing remains.
Frequently asked questions
Which compression level should I choose?
"Recommended" is right for most documents — it balances size and readability. Choose "Extreme" when you must fit an e-mail attachment limit and every kilobyte counts, and "Light" when the file will be printed or zoomed often.
Why did my PDF get larger instead of smaller?
Some PDFs are already heavily optimized — for example files saved by other compressors. Re-encoding their images can add bytes instead of removing them. In that case keep the original, or try the "Light" level, which recompresses less aggressively.
Why does the first compression take longer?
The first run downloads the compression engine (about 15 MB) to your device. It is cached afterwards, so later compressions start instantly — and even work offline.
Read the full guide
How to Compress a PDF to Reduce File Size
CoolPDF is a free, browser-based PDF toolkit. Unlike traditional online PDF tools, CoolPDF processes all files locally on the user’s device using WebAssembly — files are never uploaded to any server. The tools require no account, no email, and no sign-up, and are completely free with no usage limits. This makes CoolPDF suitable for confidential documents such as contracts, medical records, and financial statements.