Compress PDF
Shrink a PDF by re-encoding the images inside it. The text stays selectable, because the pages are never turned into pictures.
Processed on your device — no upload
How to compress PDF
- Choose the PDF you want to make smaller.
- Pick how small. Screen is for reading, Balanced suits most documents, Print keeps full resolution.
- Press compress. You will be told what it found and what it managed.
How it works
A PDF is not one thing, and where its weight sits decides what can be done about it. A scanned document is almost entirely photographs — a page image per page, often at 300 dpi because that is what the scanner defaulted to. A report written in Word is text, fonts and vector drawing instructions, with a logo somewhere.
This tool works on the first kind. It walks the file's object tree, finds every embedded JPEG, decodes it, re-encodes it at the quality you chose, and puts it back — only if the new one is actually smaller. Everything else in the document is left exactly as it was: the text, the fonts, the links, the bookmarks, the form fields, the page order.
That last part is the whole design. There is a much easier way to shrink a PDF in a browser, which is to render every page as a picture and build a new document out of the pictures. It produces spectacular numbers on a scan, and it destroys the document: text stops being text, so selection, search, copy-paste and screen readers all stop working, and on a file that was mostly text to begin with the result is usually larger than what you started with. A tool that quietly did that to your contract would have damaged it while reporting a success.
Scaling matters more than quality, and it is the setting people skip. A scanner produces an image around 3,500 pixels tall for a page that will be read on a screen at perhaps 900. Halving the dimensions quarters the pixel count before the encoder has done anything at all. Screen and Balanced both scale; Print leaves dimensions alone.
Some images are skipped deliberately. JPEG 2000 cannot be decoded by browsers. Raw Flate-compressed bitmaps depend on a colour space and bit depth that are easy to reconstruct incorrectly — and reconstructing one wrongly does not fail loudly, it produces a picture with the colours quietly wrong. Images carrying a transparency mask are left at their original size, because the mask has to keep matching them.
Everything happens in this tab. The file is read from your disk into memory, the images are re-encoded by your own processor, and the result is offered back as a download. There is no server in this to send it to.
A worked example
You have lease-signed.pdf, 8 pages, 14.2 MB — a lease you signed, scanned by an office machine at 300 dpi. Your letting agent's form rejects anything over 10 MB.
Choose the file and leave the setting on Balanced. Press Compress the PDF. It reports 8 of 8 images re-encoded and 71% smaller — 14.2 MB to 4.1 MB. Every page is still there, still the same size, and the signature is still legible.
Now the other case. You try it on quarterly-report.pdf, 2.3 MB, written in Word and exported. It comes back saying there are no re-encodable images in this file. That is the true answer: the weight is fonts and text, and nothing in a browser is going to change that. The tool says so rather than handing you a file forty kilobytes smaller and letting the percentage imply it did something.
One habit worth keeping. Compress from the original every time rather than compressing something you already compressed — JPEG loses a little on every re-encode, and those losses accumulate. The image compression guide has the detail on why.
Questions
Will the text still be selectable and searchable?
Yes. Only the embedded images are touched. The text objects, fonts and page structure are written back exactly as they were, so selection, search, copy-paste and screen readers all keep working. This is the main thing that separates it from tools that rasterise pages.
How much smaller will my file get?
It depends entirely on what is in it. A scanned document is mostly JPEG and commonly comes down by 60 to 85 per cent. A text document has almost nothing to re-encode and will barely move — the tool tells you which one you have rather than leaving you to guess from the number.
Why did nothing happen to my PDF?
Either it contains no re-encodable images, which means its size is in fonts and text, or its images are already compressed harder than the setting you picked. In the second case every re-encode came back larger and was discarded, so nothing was made worse. Try the Screen setting if the file is only going to be read on one.
Is this as good as Adobe or Ghostscript at optimising a PDF?
No, and it is worth being straight about why. Those optimise a document in ways a browser cannot: subsetting fonts, rewriting content streams, downsampling with better filters, recompressing in formats no browser can produce. What a browser does well is re-encode JPEGs, which is where a scan’s weight actually sits — so on scans the gap is small, and on text-heavy files those tools will optimize far past this one.
Does compressing a PDF reduce its quality?
The images, yes — that is how it works. Text and vectors are untouched and stay perfectly sharp at any zoom. At the Balanced setting the difference in the images is hard to see on a screen; at Screen it is visible if you zoom in on a photograph, which is the trade you are choosing.
Can I compress a PDF to a specific size, like under 10 MB?
Not directly. Run it on Balanced, look at the result, and drop to Screen if you need more. Each run starts from the original file you picked, so trying a second setting is not compounding the loss from the first.
Is my PDF uploaded anywhere?
No. The document is read from your disk into this tab’s memory and the images are re-encoded by your own processor. The site is static files with no backend, so there is no endpoint to send it to. Watch your Network tab while you use it, or disconnect from the internet and try again.
Can it reduce PDF file size for email?
That is the usual reason people compress a PDF, and a scan is exactly the case it handles best. Most mail providers cap attachments around 20 to 25 MB, and a scanned document that overshoots usually comes back well under on the Balanced setting.
Is Compress PDF free to use online?
Yes — free, with no account, no daily limit and no watermark. It runs online in your browser, and because the work happens on your own device it keeps working offline once the page has loaded.