How to Reduce PDF File Size Without Losing Quality

Everyone meets the same problem sooner or later: a PDF that is too big to email or upload. The right fix depends on what is inside the file. A method that shrinks a scan from 20 MB to 2 MB does almost nothing for a text report, and a method that keeps text perfect cannot rescue a stack of photographs. This guide helps you diagnose your file, choose the right approach and set realistic targets.

Know your limit first

Work backwards from the limit you have to meet.

• Email services commonly accept attachments of about 20 to 25 MB in total, and less if several files are attached.
• Job, visa, school and government portals often accept only a few megabytes per file, and some as little as 1 or 2 MB.
• Messaging apps and cloud forms have their own limits, which you may only discover when an upload fails.

If your file is 18 MB and the limit is 5 MB, you need to remove about 70 percent of it. That is realistic for a scan, and unrealistic for a text-only document, which tells you what to try first.

Diagnose what is making the file big

Open the PDF and try to select a sentence with your cursor.

• You can select text and the file is still big: the size probably comes from embedded images, fonts or graphics. A lossless repack may help a little, and shrinking the images at the source helps a lot.
• You cannot select text (the page highlights as one block): it is a scan, a picture of a page. It can usually be made 5 to 20 times smaller by lowering the resolution of the page images.
• A presentation exported from slides: photos and backgrounds are the cause, and they can be reduced before export.
• A design or brochure with large images: resolution matters. Screen-only use needs much less than print.

Choose the method

The Compress PDF tool offers three approaches for the common situations.

1. Lossless optimize repacks the file without touching text or images. It suits documents that need to stay searchable and selectable. Expect savings from nothing up to around a third.
2. Reduce quality redraws each page as a compressed image at 150, 110 or 72 dpi. It suits scans and image-heavy documents, and can make them dramatically smaller, but the text becomes part of the picture and can no longer be selected or searched.
3. Compress to a target size tries the lossless repack first and then lowers image quality only until the file fits under the limit you give it. It is the right choice when a form states a hard cap, and there are ready-made pages for the usual limits: 100 KB, 200 KB, 500 KB and 1 MB.

For scans, start with Medium (110 dpi), which is usually sharp enough to read, and go to Low (72 dpi) only if you must. For documents you will print, use High (150 dpi).

What resolution do you really need?

An A4 page at 72 dpi is about 595 by 842 pixels, at 110 dpi about 910 by 1,286, at 150 dpi about 1,240 by 1,754 and at 300 dpi about 2,480 by 3,508. Body text of 10 to 12 points stays legible at 110 dpi on a screen and at 150 dpi on paper. Small print, such as footnotes and legal terms, is the first thing to suffer at low resolution, so check it.

Fix the problem at the source

The best compression happens before the PDF exists.

• Scanning: use 150 to 200 dpi and grayscale for text documents. Colour and 600 dpi rarely improve readability but can multiply the size by ten.
• Photos in documents: resize and compress them before inserting. A photo displayed 10 cm wide does not need 6,000 pixels. Use the Image Resizer and Image Compressor.
• Word and Google Docs: export with the standard or minimum size option instead of high-quality print.
• PowerPoint and Keynote: compress pictures in the application before exporting, and remove unused slides and hidden layers.
• Design software: choose a screen or web preset, downsample images, and avoid embedding full fonts you only use for a few letters.

Splitting as an alternative

If a document simply has too many pages for a limit, no compression will get under it. Send it in parts with Split PDF, or remove pages that are not needed. If you have many small files and need one, Merge PDF joins them, but remember that merging does not compress. Compress the biggest inputs first.

Check the result

After compressing, open the file and check what matters: the smallest text, signatures and stamps, numbers in tables and photographs. Confirm the page count matches. If you used the image-based method, remember that links, bookmarks and searchable text are gone, so keep the original for anything that needs them.

Privacy

Files that contain personal data, such as contracts, IDs and medical records, are best compressed on your own device. The tool above works in your browser, so the file is never uploaded to a server. For a shorter walkthrough of the same task, read how to compress a PDF, and if the file also needs protection before you send it, see how to password protect a PDF.