Compress PDF
Popular HeavyReduce PDF size by re-rendering pages at a lower resolution and quality.
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Results will appear here once you run the tool.
About Compress PDF
Compress PDF reduces file size by rendering each page and re-encoding it as an image at a lower resolution and quality. Five levels run from light to extreme, or you can set resolution and quality by hand and watch what each change costs you.
This works well on scans and badly on text. A scanned document is already a series of images, so re-encoding them smaller is a straight win — often 80% or more. A born-digital PDF full of selectable text is a different story: text is stored as instructions to draw glyphs, which is far more compact than a picture of those glyphs. Compressing it can make the file larger.
The tool checks, and tells you. If the compressed result comes out bigger than the original, you are told to keep the original rather than being handed a worse file with a success message. Greyscale conversion is there for scans of black-and-white paper, where the colour channels are recording nothing but the scanner noise.
The trade-off you are making: because pages become images, selectable text and any text layer are lost. Search, copy-paste and screen readers stop working on the result. If you need the text preserved, compress lightly or not at all.
It runs on your machine. Rendering every page of a long PDF takes real processor time — a hundred-page document is not instant. In exchange, a confidential file never gets uploaded to anyone, and there is no size limit or daily quota.
How to use Compress PDF
- Add your PDF. Drop in one or more documents — up to 100. Compression works best on scans and image-heavy files.
- Pick a compression level. Start with balanced. Move to strong or extreme if the file is still too big, or switch to custom to set resolution and image quality yourself.
- Consider greyscale. If the document is a scan of black-and-white paper, converting to greyscale removes colour channels that are only recording scanner noise.
- Run it and check the result. Press Run. You are shown the before and after size. If the result came out larger — which happens with text-heavy PDFs — you are told to keep your original.
Frequently asked questions
Why did my PDF get bigger instead of smaller?
Compression works by rasterising each page into an image. For a text-heavy PDF that is already efficiently encoded, images are larger than the text they replace. The tool detects this and tells you to keep your original. Compression pays off on scans and image-heavy documents, which is where large files usually come from.
Will the text still be selectable afterwards?
No. Because pages are re-rendered as images, the text layer is lost. If you need selectable text, use a lower compression level on a scan, or keep the original.
Are my files uploaded when I use Compress PDF?
No. Compress PDF runs entirely inside your browser. Your file is read locally, processed on your own device, and handed straight back to you. You can confirm this yourself: open your browser's developer tools, watch the Network tab, and run the tool — no request carries your data anywhere.
Is Compress PDF free?
Yes, completely. No account, no sign-up, no watermark on your output, and no cap on how many times you can use it. The project is open source under the AGPL licence.
Is there a file size limit?
There is no server limit, because nothing is uploaded. The practical ceiling is your device's memory — on a modern laptop, files up to a few hundred megabytes are comfortable, while phones handle less. If a tab becomes unresponsive, the file was too large for the memory available.
Can I process several files at once with Compress PDF?
Yes — up to 100 at a time. When there are more than a few results they are packaged into a ZIP so you get everything in one download.
Why does this take a while?
The work happens on your device rather than a server, so speed depends on your own processor. That is the trade for never uploading anything. Larger files and higher quality settings take proportionally longer.
Does Compress PDF work offline?
Mostly. The site caches itself after your first visit, so it keeps working without a connection. Tools that need a specialised library — PDF editing, OCR, QR codes, MP3 encoding — need a connection the first time you run them, then that library is cached too.