How to reduce PDF file size
A ten-page PDF can weigh 200 KB or 50 MB depending on what's inside. When a file is too big to email or upload, knowing why it's big tells you the fastest way to shrink it — and how much quality you're willing to give up.
Why PDFs get big
- Photos at full resolution. A single smartphone photo can be several megabytes. Insert ten into a document and export it, and the PDF carries all of them.
- Scans. Each scanned page is an image. Scanning in color at high resolution produces very large files, even when the page is just black text on white paper.
- Embedded fonts. Usually small, but documents that use many fonts, or fonts with large character sets, add up.
- Merged files. Combining PDFs adds their sizes together, and repeated elements such as logos may be stored more than once.
- Extras: attachments, form data, high-resolution vector drawings or embedded previews.
Text itself is tiny. If a PDF is mostly text and still large, images are almost always the reason.
How small does it need to be?
Many email services cap attachments at around 20–25 MB, and online forms (job applications, government portals) often allow much less — sometimes 2–5 MB per file. Check the limit first: it decides whether a gentle optimization is enough or you need to split the file.
Ways to make it smaller
1. Export again with smaller images
If you have the original document, this gives the best result:
- Word: select a picture, choose Compress Pictures and apply a lower resolution to all pictures; then when saving as PDF, choose Minimum size (publishing online).
- LibreOffice: in File → Export as PDF, use JPEG compression and reduce image resolution (for example to 150 DPI for screen reading).
See how to save a Word document as PDF for the other export options worth checking.
2. Preview on a Mac
Open the PDF, choose File → Export and select the Reduce File Size Quartz filter. It's very effective but can reduce image quality quite aggressively, so check the result before sending.
3. Rescan with better settings
For scanned documents, the scan settings matter most:
- Use grayscale or black-and-white for text documents instead of color.
- Use 200–300 dpi; 600 dpi is rarely needed for documents.
- Let the scanner save as PDF directly rather than as individual large images.
If you'll also want to search or copy the text, see scanned PDFs and OCR.
4. Dedicated compression tools
- Paid PDF editors such as Adobe Acrobat include "reduce file size" or "optimize PDF" features with fine control over what's compressed.
- Ghostscript, a free open-source command-line tool, can recompress a PDF with presets for screen, e-book or print quality.
- Online compressors are convenient but upload your file to a server; think twice with sensitive documents (see are online PDF tools safe?).
5. Send less
Often the simplest fix is to not send everything. Extract only the pages that are needed, or split the document into two or three parts that each fit the limit.
How much quality can you give up?
| Purpose | Image resolution that's usually enough |
|---|---|
| Reading on screen | About 150 dpi |
| Printing at home or in an office | About 200–300 dpi |
| Professional printing | 300 dpi or more — don't compress aggressively |
Always open the compressed file and zoom in on photos, small print and signatures before sending. A file that fits the limit but can't be read defeats the purpose.
Quick checklist
- Find the size limit you need to meet.
- If you have the source document, compress images and re-export.
- For scans, rescan in grayscale at 200–300 dpi.
- Otherwise, use Preview (Mac) or a compression tool.
- If it's still too big, split the file or send only the necessary pages.
- Check readability of the final file.
Too many pages? Extract only what you need or split the PDF into smaller files, privately in your browser.
Open Split PDF