Quick answer: Compressing a PDF reduces its file size by re-encoding the images and page data inside it. Pick a level, the tool re-renders the pages smaller, and you download a lighter file. It works best on scanned and image-heavy PDFs, which often shrink by half or more.
How to compress a PDF in three steps
- Choose your PDF. The tool shows its size and page count first.
- Pick a level and resolution. Balanced suits most documents; Strong saves the most; grayscale suits scanned text.
- Compress and download. You see the original size, new size and percentage saved. If the file would grow, the tool offers the original instead.
How the browser-based compressor works
It renders each page with PDF.js, re-encodes each page as a JPEG at your chosen quality and resolution, and rebuilds the PDF with pdf-lib, all in your browser. That is very effective where images make the file large, and much less so on text, which is already compact.
What this tool can and cannot do
| Document type | Typical result |
|---|---|
| Scanned pages, photos, brochures | Often 50 – 80% smaller |
| Mixed text and images | Usually 20 – 50% smaller |
| Plain text, exported reports | Little change, sometimes larger |
| Already-compressed PDFs | Little to no further saving |
Files up to about 50 MB or 200 pages are comfortable on a desktop; a phone manages less, and the tool warns you first.
Know the trade-off: Pages become images, so text is no longer selectable or searchable, and locked PDFs cannot be opened until the password is removed. Keep your original if you need editable text or full print resolution.
Why use this compressor
- Processed on your device: sensitive documents never travel.
- You control the trade-off: quality, resolution and colour are separate settings.
- No watermark or signup, and no cap on files.
- Any modern browser on desktop or mobile.
When you need to compress a PDF
- Email limits: most providers cap attachments around 25 MB.
- Application portals with strict file-size caps.
- Faster sharing and storage on cloud drives and phones.
- Scanned documents, the best case for this tool.
Privacy
The file is read, re-rendered and rebuilt entirely in your browser. It is not uploaded or stored and no account is needed. Site analytics are covered in our privacy policy.
Frequently asked questions
Is the Compress PDF tool free?
Yes, with no signup, watermark or cap on files. The limit is your device’s memory.
Are my files uploaded?
No. The PDF is read and rebuilt inside your browser tab and never transmitted.
How much smaller will my PDF be?
Scanned and image-heavy PDFs often shrink 50 to 80%. Mostly-text documents may barely change.
Why did my PDF get bigger?
Pages become images, and an image of text is larger than the text. The tool detects this and offers the original instead.
What is the largest PDF I can compress?
Roughly 50 MB or 200 pages on a desktop, less on a phone. The tool warns you before starting.
Does the compressed PDF keep selectable text?
No. Pages become images, so text is no longer selectable or searchable.
What does grayscale do?
It removes colour from every page, often cutting another third off a black-and-white scan with no visible change.
Can I compress a password-protected PDF?
Not until the password is removed.
Other PDF tools
Accuracy note: Compression behaviour is described from how the tool actually works, including the cases where it does not help.
Content Lead, Anchor AI Tools, California, USA. Spotted an error? Email hello@anchoraitools.com and it will be checked and corrected. See our editorial standards.