How to Compress a PDF Without Losing Quality
By Bishal Neupane · · Updated · 5 min read
A PDF that's too big to email or upload is almost always full of images: scanned pages or photos. Compressing those images the right way can cut the file to a fraction of its size while the text stays perfectly sharp.
What makes a PDF big, and why scans shrink most
- Scanned pages. Every page of a scan is a picture, often saved at 300-600 DPI, so a few pages can run to many megabytes.
- Photos. Pictures from phones and cameras are several megabytes each.
- Text and vector graphics are tiny by comparison. A 50-page report without images is often under 1 MB.
That is why a scan or a photo-heavy PDF can shrink by half or more: resampling a 300 or 600 DPI page down to 150 DPI removes most of its pixels. A PDF exported from a word processor is mostly text and vector shapes, which are already compact and are never touched, so it changes little. If a mostly-text PDF is still too big, look for large embedded photos, or drop pages with Remove Pages.
Compress a PDF step by step
- Open Compress PDF and add one or more PDFs.
- Choose a level: Low, Recommended or Extreme.
- Click Compress PDF. The result shows how much smaller the file got.
- Download the compressed PDF. Several files download together as a ZIP.
Large images are resampled to the level's resolution and saved as JPEGs, then the rest of the file is recompressed without any loss. Text, fonts and vector drawings aren't touched, and a file is never made bigger. Everything happens in your browser, so nothing is uploaded.
Which level should you choose?
Text, fonts and vector graphics stay exactly as they are at every level, so words are as sharp as before. Only images change. Each level has a threshold: an image is resampled only if it is above the threshold resolution, and then it is brought down to the level's target and saved as a JPEG. Images already at or below the threshold are left alone, and an image is only replaced when the new version is clearly smaller.
- Low is closest to the original. Images above 300 DPI are resampled down to 220 DPI, with high JPEG quality; anything at or below 300 DPI is left as it is. Use it for documents you'll print.
- Recommended resamples images above 200 DPI down to 150 DPI. It is the best balance for email, WhatsApp and upload portals, and on a normal screen most pages look the same.
- Extreme resamples images above 120 DPI down to 96 DPI with stronger JPEG compression. It is fine for reading on screen, but small print in scans may look softer.
So "no quality loss" is true for text and vector artwork, while photos and scans trade a little detail for size. Compare the result with the original before you send it, and keep the original.
Compress on your phone or computer, with no install
Compress PDF runs in the browser, so the same steps work on a laptop, an iPhone or an Android phone. There is no app to install and no account. Because the images are re-encoded on your own device, a payslip or a signed contract never leaves it, which matters for documents you would think twice about uploading elsewhere.
A few practical points. You can add several PDFs at once and get a ZIP back. On a phone, the result lands wherever your browser saves downloads, and our guide to where downloaded PDFs are saved on iPhone and Android shows how to find it. If the file is meant for email, check the new size against the mail limit in how to send a large PDF by email.
Need a specific size, like 300 KB?
Upload portals often state an exact limit. Choose Target file size in Compress PDF and pick or type the limit; the tool tries progressively stronger settings and keeps the sharpest version that fits. There are ready-made pages for common limits: 50 KB, 100 KB, 150 KB, 200 KB, 300 KB, 400 KB, 500 KB, 1 MB and 2 MB.
Still too big?
- Remove pages nobody needs with Remove Pages.
- Cut the file into parts under a size limit with Split by Size and send them separately.
- Rescan at 200–300 DPI instead of 600. It's still sharp and far smaller.
Compress last: merge, sign and edit first, then compress the final file once.
Common problems and fixes
- The file barely got smaller.
- It probably contains mostly text, which is already compact, or its images are already compressed. Try Extreme for scans; for text documents, removing pages is the only way to make it much smaller.
- Images look blurry after compressing.
- Use Low, which only resamples images above 300 DPI (down to 220 DPI), or Recommended if you used Extreme.
- It says the PDF is password-protected.
- Remove the password with Unlock PDF first, compress, then add it back with Protect PDF if you need to.
- Colours in a photo look slightly different.
- Recompressed images are saved as standard RGB JPEGs. CMYK images, used in print-ready files, are left exactly as they were; for press work, use Low or skip compression.
Frequently asked questions
No. Text, fonts and vector graphics stay exactly as they are; only large images are resampled.
Yes. Add them together; each one is compressed separately and they download as a ZIP.
No. Compression runs in your browser, on your device.
Scans and photo-heavy PDFs often shrink by half or more. Text-only PDFs change little because they're already small.
Text and vector graphics are never changed, so they stay sharp. Images are resampled, so a little detail is traded for size. Low keeps images closest to the original: only images above 300 DPI are resampled, to 220 DPI. It is the safest choice for printing.
They set how far images are reduced. Low resamples images above 300 DPI to 220 DPI, Recommended resamples images above 200 DPI to 150 DPI, and Extreme resamples images above 120 DPI to 96 DPI with stronger compression. Images at or below a level's threshold are left as they are.
It has few or no large images, and text is already compact. To make it smaller, remove pages you don't need with Remove Pages.