How to Compress a PDF Without Losing Quality
What PDF compression actually does under the hood, how much smaller you can realistically expect a file to get, and when to leave it alone.
A PDF's file size mostly comes down to one thing: images. Scanned documents, screenshots pasted into a report, or a brochure exported "for print" instead of "for screen" can turn a 10-page PDF into a 40 MB file that bounces off every email server and upload form. Compression fixes that, but "without losing quality" means different things depending on what is inside the file. This guide explains what compression actually does, how much smaller you can realistically expect a file to get, and how to choose settings you won't regret.
What makes a PDF big
A PDF is a container. Text is stored very efficiently: a page of text is only a few kilobytes, even with its fonts embedded. Images are where the weight is. A single A4 page scanned at 300 DPI is roughly 2,480 × 3,508 pixels, and a scanner that saves it with light compression can easily produce 1–3 MB per page. Multiply by 20 pages and you have a file no email will carry.
Smaller contributors include fully embedded fonts (rather than only the characters used), metadata and editing leftovers that design applications write into the file, and duplicated resources when the same logo is stored separately on every page.
Two kinds of compression
Good compressors are honest about which kind they are doing, because the trade-offs are completely different.
Lossless cleanup
This rewrites the file's internal structure more efficiently and removes data nobody sees: metadata, editor scratch data and redundant objects. Every pixel and every character stays exactly as it was. The saving is modest, usually 5–20%, because that is all the waste a well-formed PDF contains. Choose it when the file must stay pixel-perfect: signed contracts, technical drawings, anything going to a professional printer.
Image re-encoding
This is where the dramatic reductions come from. Each page is re-rendered as an image at a resolution you choose and stored with JPEG compression. A scan at 300 DPI re-encoded at 150 DPI is a quarter of the pixels, and on a screen it looks the same. Scanned documents routinely shrink by 60–90% this way, and image-heavy brochures by 50–70%.
The cost is that the page becomes an image. Text on a re-encoded page is no longer selectable or searchable, and very small print softens at low resolutions. Any tool promising "90% smaller with no quality loss" is doing this without telling you.
How to compress a PDF
- Open the Compress PDF tool and add one file or a batch. Each file's original size and page count are shown straight away, giving you a baseline.
- Choose a level. Lossless cleanup keeps everything intact. Balanced re-encodes pages at 150 DPI and suits almost everything. Strong and Maximum go further for strict size caps. Custom gives you the DPI and JPEG quality sliders directly.
- If a portal has a hard limit, enter a target size and let the tool find settings that fit. You can also convert to grayscale (a big saving on scans of black-and-white documents) and strip metadata.
- Compress and compare. Each file shows its original and compressed first page side by side with exact byte counts and the percentage saved. If the result is too soft, run it again at a gentler level.
The compression runs in your browser, so the file is never uploaded, which matters when the PDF is a payslip or a medical report. There is no file size limit beyond your device's memory, and batches can be downloaded individually or as a ZIP.
How much smaller can you expect?
| Type of PDF | Typical saving |
|---|---|
| Scanned documents and phone photos of pages | 60–90% |
| Brochures, slide decks and image-heavy reports | 50–70% |
| Text documents exported from Word or Google Docs | 5–20% |
| A PDF that was already compressed | Little or nothing |
If a file barely shrinks, that is usually good news: it was already well optimised. Compressing it harder will only damage it.
Choosing a resolution
- 72–100 DPI: fine for on-screen reading of large text; small print and footnotes start to blur. Use it only to squeeze under a strict cap.
- 150 DPI: the sweet spot. Body text is comfortably readable on screen and prints acceptably on an office printer.
- 200–300 DPI: for documents that will be printed and read closely, or scans with fine detail such as signatures and stamps.
When you should not compress
If the PDF will be printed at a large size, or contains diagrams and small text inside images (a scanned technical drawing, a map, a lab report with tiny figures), aggressive compression can make fine detail unreadable. For anything print-critical, compress a copy and check it at 100% zoom before sending. Never compress the only copy you have.
Also think twice about compressing a document that must stay searchable, such as a long contract someone will need to search through later. Use lossless cleanup there, or keep a searchable original alongside the small copy.
Other ways to get under a size limit
- Send fewer pages. If the recipient needs pages 1–6 of 40, extract those pages instead of compressing the whole thing.
- Fix the source. If you made the PDF yourself, export it again with "minimum size" or "standard (online)" settings. That beats compressing a bloated export.
- Shrink photos before they become a PDF. When building a PDF from phone photos, run them through the Image Compressor first, then convert with JPG to PDF.
- Share a link instead. For files that are big because they need to be, an encrypted file transfer avoids attachment limits entirely.
Frequently asked questions
Will the text still be searchable after compression?
With lossless cleanup, yes, because nothing is changed. With image re-encoding, the page becomes an image, so text is no longer selectable. For a scanned document that never had real text, nothing is lost either way.
Why is my compressed PDF bigger than the original?
A file of mostly text and vector graphics can grow if it is re-rendered as images, because a picture of text is heavier than the text itself. Use lossless cleanup for those files.
How small does a PDF need to be for email?
Gmail allows attachments up to 25 MB and many company mail servers stop at 10–20 MB. Government and job portals are often stricter, at 1–5 MB, which is where the target-size option is most useful.
Can I compress several PDFs at once?
Yes. Add them all and they are compressed one after another with the same settings, each with its own before-and-after report.
Last updated
October 12, 2026