Compress a PDF
This tool rebuilds a PDF as a series of JPEG images at the resolution and quality you choose. That is what almost every "compress PDF" service does, and it works spectacularly well on scans — often 80–95% smaller. The honest trade-off: the pages become pictures, so any selectable text is lost. Read the note below before using it on a text document.
How to use the Compress PDF
- Drop the PDF you need to shrink.
- Pick a resolution: 120 DPI is comfortable on screen, 150 DPI still prints acceptably.
- Drag the JPEG quality slider — 60–70% is the sweet spot for scanned paper.
- Click Compress PDF and compare the before/after sizes shown under the button.
How this compression works
Each page is rendered by PDF.js at the DPI you choose, exactly as a viewer would draw it, then encoded as a JPEG and placed into a new PDF at the original page dimensions. The output therefore has the same number of pages, the same paper size and the same visual layout — but every page is now a photograph of itself. Two settings control the size: resolution decides how many pixels each page gets, and JPEG quality decides how hard those pixels are compressed. Halving the DPI removes about three quarters of the pixels, so it is the bigger lever.
What you gain and what you lose
| Preserved | Lost |
|---|---|
| Page count, page size, visual appearance | Selectable and searchable text |
| Reading order for a human | Hyperlinks, bookmarks, form fields |
| Colour (unless you tick greyscale) | Fine hairlines and tiny type at low DPI |
If you need the text layer — for search, for accessibility, or because a solicitor or a recruiter will copy from it — keep the original and send that instead, or split the difference: compress the scanned appendix and merge it back onto the text pages with Merge PDF.
When it will not help
A PDF exported from Word that is already 300 KB of pure text will usually get bigger, because prose compresses far better as font instructions than as pictures of letters. The result box tells you the before and after size and says plainly when there was no saving, so you can discard the output. Files that are large because of one enormous embedded photograph are better handled by recompressing that image before export.
Picking a setting
- E-mail a 40 MB scan: 96 DPI, quality 60, greyscale on. Expect 1–3 MB.
- Upload to a portal with a 5 MB limit: 120 DPI, quality 65.
- Keep it printable: 150 DPI, quality 80. Still typically 60–80% smaller than a 300 DPI scan.
Everything happens on your device, so there is no upload wait and no copy of a confidential scan sitting on someone's server. A 100-page document takes roughly 15–40 seconds depending on your machine.
Frequently asked questions
Will my text still be selectable after compressing?
No. This method re-renders every page as an image, so text becomes part of the picture. That is true of most free "compress PDF" tools, whether or not they say so. Keep the original if you need the text layer.
How much smaller will my file get?
Scans typically drop by 80–95%. Text-only PDFs exported from a word processor may not shrink at all — the tool tells you when there was no saving.
Which setting should I use for e-mail?
96 DPI at quality 60, with greyscale on for black-and-white paperwork. That usually brings a 40 MB scan under 3 MB.
Is my document uploaded?
No. Rendering and re-encoding both happen in your browser; the file never leaves your device.
Privacy
This tool runs entirely inside your browser using WebAssembly and the Canvas/File APIs. Your files are never uploaded to ToolFlint or any third party; you can verify this in your browser's network tab or by switching to airplane mode after the page loads. Read how we process files.
Last updated 2026-09-23.