How to Compress a Scanned PDF
A scan is a stack of photographs, so ordinary PDF compression barely helps. Downsampling to 150 DPI and greyscale typically cuts 80–95%.
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PDF Compressor — Shrink PDFs in Your Browser
Compress PDFs without uploading them. Lossless rebuild keeps text selectable, or downsample scanned pages to cut file size by up to 95%.
- Runs entirely in your browser
- No uploads, no servers
- Free, no signup
Drop a PDF here, or
PDF files · Compressed on your device · Nothing is uploaded
150 DPI is the usual choice for a document you email.
70–80% is usually indistinguishable on a document.
About this tool
Drop in a PDF and compress it on your own device — no upload, no queue, no watermark. Choose a lossless rebuild that keeps text selectable and changes nothing you can see, or downsample the pages for scanned documents, where the real savings are. Because everything runs in your browser, contracts, payslips and medical letters never leave your computer.
The method you want depends entirely on why your PDF is large, and the two cases need opposite approaches.
A PDF exported from Word, Pages or a design tool is mostly text and vector graphics with some structural overhead. Lossless rebuild is the right choice — it strips duplicated fonts, unused objects and an inefficient cross-reference table, typically saving 5–30% with nothing whatsoever changed on screen.
A PDF from a scanner or a phone camera is a stack of photographs. No amount of lossless work helps, because there is no redundancy to remove. Downsampling the pages to 150 DPI routinely cuts these by 80–95%, which is the difference between a file that will not attach to an email and one that sends instantly.
If you are not sure which you have, run lossless first. A disappointing result tells you it is a scan.
For the reasoning behind the DPI and quality numbers, see how to compress a scanned PDF, and why PDFs get large in the first place covers diagnosing it from the file size per page.
What it does
- Lossless rebuild — text stays selectable
- Downsample scanned pages at 96–300 DPI
- Optional greyscale conversion for colour scans
- Adjustable image quality
- Batch up to 10 PDFs at once
- Nothing uploaded — runs entirely on your device
Frequently asked questions
Are my PDFs uploaded anywhere?
No. The compression engine runs in your browser using WebAssembly. You can disconnect from the internet after the page finishes loading and the tool still works — which is the clearest proof that nothing is being sent. This matters more for PDFs than for most files, because contracts, payslips and medical records are exactly what people need to compress.
Which compression method should I choose?
Try lossless rebuild first — it keeps text selectable and never changes how the document looks. If it barely helps, your PDF is made of scanned images, and downsample pages is the method that will actually shrink it.
Why did lossless rebuild barely save anything?
Because your PDF is mostly images. Lossless rebuild removes duplicated objects and unused data, which helps documents bloated by their generator. In a scanned PDF each page is a photograph, and the only way to shrink it is to re-encode those images.
Will I lose the ability to search or select text?
Only with the downsample method, which replaces each page with an image. Lossless rebuild preserves everything. If you need both a small file and selectable text, run OCR on the result afterwards.
What DPI should I use?
150 DPI for anything you might print on an office printer, and it is the right default for emailing a document. Drop to 96 DPI for screen-only reading. Use 200–300 DPI if the document has small print or fine detail you need to stay legible.
Why will my password-protected PDF not compress?
Encrypted PDFs cannot be read without the password, and the tool does not ask for one. Open the file in your PDF reader, save an unprotected copy, and compress that instead.
Is there a file size limit?
Files up to about 100MB work. Very large scanned documents are processed page by page, so a long file takes time but will not run out of memory.
Last updated .