Quick answer: Most of a PDF’s size comes from images, so the biggest saving comes from lowering image resolution to what the document needs: about 150 dpi for screen and email and 300 dpi for print. Compress the file, then zoom to 100% and 200% to check text and photos. For sensitive files, use a browser-based compressor so the document never leaves your device.
What makes a PDF file large
| Cause | Why it adds size | Fix |
|---|---|---|
| High-resolution photos | A 12 MP photo can be several MB on its own | Downsample images to 150 dpi for screen |
| Scanned pages | Each page is a full-page image | Scan at 200 to 300 dpi in grayscale for text |
| Embedded fonts | Full font files are stored inside the PDF | Subset fonts when exporting |
| Duplicate or hidden content | Layers, thumbnails, form data, metadata | Flatten and remove unused objects |
| Uncompressed exports | Some apps save with little compression | Re-save or compress the PDF |
How to compress a PDF, step by step
- Open the Compress PDF tool and add your file. It is processed in your browser.
- Choose a level: light for print, balanced for email, strong for web forms with tight limits.
- Compress and compare the new size with the original.
- Check the result at 100% and 200% zoom, especially small text, signatures and photos.
- Try one level lighter if anything looks blurred, and keep the original.
Size targets for common uses
| Where it is going | Typical limit or goal | Suggested setting |
|---|---|---|
| Gmail attachment | 25 MB | Balanced |
| Outlook email attachment | 20 MB | Balanced |
| Job and government portals | Often 2 to 10 MB | Strong, then check legibility |
| Website download | As small as legible | Balanced or strong |
| Professional print | Quality over size | Light, keep 300 dpi images |
Choose the right image resolution
| Use | Image resolution |
|---|---|
| Viewing on screen, email | 150 dpi |
| Office printing | 200 to 300 dpi |
| Professional print | 300 dpi |
| Line drawings and fine text scans | 300 dpi, black and white |
Halving the resolution cuts the pixel count to a quarter, which is why going from 300 to 150 dpi often shrinks an image-heavy PDF by 60 to 75%.
Scanned documents
- Scan text in grayscale or black and white, not color. Color scans are several times larger.
- 200 to 300 dpi is enough for legible text.
- Crop margins and remove blank pages before saving.
- Merge scans once rather than re-saving repeatedly.
Other ways to make a PDF smaller
- Split the PDF and send only the pages needed.
- Export again from the source (Word, Google Docs) with a smaller size or “optimize for web” option.
- Convert photo-heavy pages to JPEG images at 150 dpi with the PDF converter, then rebuild.
- Remove attachments and form data you do not need to send.
How to check you did not lose quality
- Zoom to 100% and read the smallest text.
- Zoom to 200% on photos, logos and signatures.
- Print one page if the file will be printed.
- Confirm links and form fields still work if the document relies on them.
Frequently asked questions
How do I reduce a PDF file size without losing quality?
Lower image resolution only as far as the use needs, 150 dpi for screen and 300 for print, and keep text as text. Check the result at 100% and 200% zoom.
Why is my PDF so large?
Usually because of high-resolution images or scanned pages. Embedded fonts and extra data add more.
How can I compress a PDF for email?
Use a balanced compression level to get under 20 MB for Outlook or 25 MB for Gmail, and check the result.
Can I compress a PDF without uploading it?
Yes. Browser-based tools such as Compress PDF on this site process the file on your device.
Does compressing a PDF remove text?
It should not. Text stays text; compression mainly affects images. Always check the output.
What if the PDF is still too big?
Split it and send only the needed pages, or re-export from the original document at a lower image resolution.
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Content Lead, Anchor AI Tools, California, USA. Spotted an error? Email hello@anchoraitools.com and it will be checked and corrected. See our editorial standards.