Compress PDF

Two kinds of compression

PDFs get big for different reasons, so the tool offers two levels.

Recommended is lossless. It looks for waste inside the file and removes it:

• objects nothing points to any more, often left behind by earlier edits
• byte-for-byte duplicates, such as the same logo or font stored once per merged file
• embedded page thumbnails and private editing data that PDF readers never show
• streams that were saved without any compression

It then packs the many small pieces of the file into compressed blocks. Text, vector graphics and images are not touched, so the result looks exactly like the original.

Strong redraws every page as a JPEG picture at the resolution you choose, then builds a new PDF from those pictures. This shrinks scans and photo-heavy files dramatically. The price: text in the result cannot be selected, searched or copied, and links no longer work.

Which level should I use?

You can run the same files again with the other level. Changing a setting resets the results so you can compare.

Choosing resolution and quality

Resolution is how many dots are drawn per inch of page. Quality controls how hard each JPEG is squeezed. Strong compression offers three resolutions and a quality slider from 10% to 95%; it starts at 100 dpi and 60%.

The pixel sizes come from page size in inches × dpi. An A4 page is 8.27 × 11.69 inches, so at 150 dpi it becomes about 1,240 × 1,754 pixels. Doubling the dpi roughly quadruples the number of pixels, which is why 150 dpi files are much larger than 72 dpi ones.

For quality, 50–70% is a sweet spot for scanned documents. Below about 40%, blocky patterns appear around letters.

Worked example

A 12-page scanned rental application is 18.4 MB, and the agent’s portal only accepts files under 5 MB.

1. Add the PDF and choose Recommended. The result is 18.1 MB: a scan is all pictures, so lossless clean-up saves little. The tool says so.
2. Switch to Strong, keep 100 dpi and set quality to 60%. Click Compress again.
3. The file line now reads “18.4 MB → 2.1 MB · 88.6% smaller”. That fits the portal, and the text is still easy to read.

Your numbers will differ, because savings depend on the scanner settings and the content of the pages.

How to compress a PDF to 100 KB, 200 KB or 500 KB

Job, exam and government portals often set small limits like these. If you just want a file under a fixed limit, the preset pages search for the right settings for you: compress PDF to 100KB, 200KB, 500KB or 1MB. On this page you choose a level, a resolution and a quality, and it shows the new size. With a few tries you can usually land under a limit. The key is to think in kilobytes per page.

A text PDF exported from Word can often fit a small budget with Recommended, because text is stored very efficiently. A scanned page is a picture, and pictures cost far more. Even at the lowest settings, a readable scanned page usually needs tens of kilobytes, so the bottom-right corners of the table (10 KB or less a page) are rarely reachable for scans.

Steps for a scanned document:

1. Try Strong at 100 dpi and 60% first, and note the size.
2. Still too big? Switch to 72 dpi. That draws about half as many pixels as 100 dpi.
3. Then lower the quality in steps of 10%, down to about 40%. Zoom in on the result each time: if small print blurs, go back one step.
4. Divide the new size by the number of pages to see your real cost per page, and compare it with your budget.

Example: a 3-page scanned form must be under 200 KB, a budget of about 67 KB a page. Say Strong at 100 dpi and 60% gives 390 KB, or 130 KB a page. Moving to 72 dpi roughly halves the pixels, so the next try should land somewhere near 200 KB; lowering quality to 50% then takes it under. Every scan is different, so check the size the tool reports rather than trusting the estimate.

When a long scan cannot reach 100 KB:

• Delete pages you do not need, such as blank backs and duplicate copies, with Delete PDF Pages.
• Split the file into parts that each fit, if the portal accepts more than one upload. Split PDF does this.
• Rescan in grayscale at a lower resolution. Grey pages usually compress better than colour ones, and this tool keeps colour as it is.

If your file must be a very small size and has many scanned pages, the honest answer is that it may not fit in one file while staying readable.

How to compress a PDF without losing quality

Choose Recommended. It is lossless: it only removes data that nobody sees and packs the rest more tightly. Every letter, line and image stays exactly as it was, text stays searchable and links keep working.

Strong always loses something. Text becomes part of a picture, and JPEG compression drops fine detail. At 150 dpi and 80–95% quality, scans can look almost the same as the original on screen, but the file will not shrink as much.

Compressing a PDF on iPhone and Android

The tool runs in your phone’s browser, so there is no app to install. On iPhone, open this page in Safari, tap the box, then tap Browse to pick the PDF from the Files app or iCloud Drive; the smaller copy goes to the Downloads folder in Files. On Android, open the page in Chrome and pick the PDF from Downloads or Google Drive. Large scans take longer on a phone than on a computer, because all the work happens on your device. For Mac Preview, Windows and phone-specific steps, see our guide on how to compress a PDF on iPhone, Mac and Windows.

Email and upload size limits

At the time of writing, these are the attachment limits most people run into. Providers change them from time to time, so check their help pages if you are close to a limit.

Email attachments are encoded for sending, which adds roughly a third to their size, so aim well under the limit. A 20 MB PDF can count as more than 25 MB once encoded.

Why a PDF sometimes will not shrink

If the compressed file is not smaller, the tool keeps the original and labels it “already well compressed”. This happens with PDFs that were optimized when they were created, and with text-only files under Strong compression, where a page picture is bigger than the text it replaces. You never download a file that grew.

More ways to cut the size

• Remove pages you do not need with Delete PDF Pages before compressing.
• Send it in parts. Split PDF breaks a long document into smaller files.
• Shrink photos before making a PDF. Compress Image reduces JPGs, then JPG to PDF turns them into one document.

Privacy

Everything happens on your device. The PDFs are read by your browser, compressed in memory and offered as downloads. They are never uploaded, which makes the tool suitable for ID scans, contracts and medical records.