How to reduce a PDF's file size without ruining it
Short answer: A large PDF is almost always large because of the images inside it — scans or photographs at full resolution. Compressing those images, while leaving the text as real text, shrank colour scans by 39–86% in our tests. Black-and-white scans and PDFs that are mostly text are already compact and barely change; split those instead if they are still too big.
Updated
Why your PDF is so big
Text is cheap. A hundred pages of plain text, with its fonts embedded, is often well under a megabyte. What makes a PDF heavy is almost always images:
- Scanned pages, where every page is a photograph of paper — often at printer resolution.
- Photographs placed in a report or brochure at their full camera size.
- Presentations exported to PDF with every slide background kept at full quality.
That is also why compression results vary so widely. The saving comes from the images, so the more of the file is images, the more there is to save.
How to compress a PDF
- Open Compress PDF.
- Add your PDF.
- Choose a level: Balanced suits almost everything; Light keeps print-quality images; Strong makes the smallest file for documents that will only be read on screen.
- Compress, and download the smaller file.
The pages are not turned into pictures, which is a shortcut some compressors take to produce a bigger number. Only the images inside the pages are recompressed, so text stays selectable, searchable and sharp at any zoom, and every page keeps its size and order.
| Level | Images come out | Use it for |
|---|---|---|
| Light | Close to print quality | Documents that will be printed |
| Balanced | Screen resolution | Email, upload forms, most sharing |
| Strong | Smallest that still reads well on screen | Hard size limits, screen-only reading |
What to expect
In our test of 14 real documents, colour scans dropped by 39–86% at the Balanced setting. Black-and-white scans, text-heavy reports and e-books from professional publishing software lost only a few percent, because there was little to remove in the first place. If a file is already as compressed as the chosen level allows, it is handed back unchanged rather than made bigger.
Document properties such as author and title are removed as part of the process, both because they take space and because they are often more revealing than people expect. Bookmarks and links are kept.
Common size limits
The usual reason to compress is a limit somebody else sets. Gmail accepts attachments up to 25 MB in total and Outlook.com 20 MB; many job application, visa and university portals cap uploads far lower, often at 2–10 MB per file. Check the limit first, then pick the compression level that gets under it with the least loss.
When compression is not enough
- Split it. Split PDF extracts a page range or produces one file per page, so a long document can be sent in parts.
- Rescan at a lower resolution. 150–200 DPI is plenty for reading on screen; 300 DPI is only needed for print.
- Shrink the images before they go in. If you are building a PDF from photos, compress the images first, then combine them into a PDF.
- Remove pages nobody needs — blank scanned backs of pages are a common culprit.
Password-protected PDFs cannot be compressed until the password is removed. Unlock the PDF with its password first, then compress it.