Compress PDF

Reduce PDF size by level or to an exact size in KB for upload limits, without uploading the PDF.

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Processed in this browser · up to 50 at a time

Compress by

Level

LosslessBalancedStrong

Images finer than 150 DPI on the page are scaled down to it, and images are saved again as JPG at quality 75 where that makes them smaller. Text and drawings are not changed.

Greyscale images

Makes PDFs smaller: a scanned certificate for a portal that takes 200 KB, a statement for an email attachment, or photos that went into a PDF at full size. Choose a level, or the size the file must fit, and the tool says what it changed and how much it saved. You can read the pages at 100% before downloading, to check the text is still sharp. The PDFs are compressed on your device and never uploaded.

How to use it

Add one or more PDFs; each is compressed on its own. A PDF that needs a password asks for it, and the compressed file has no password.

Level: Lossless, Balanced (the default) or Strong, described under How it works.
Target size: the largest the file may be, in KB, and optionally the smallest. The maximum counts 1 KB as 1,000 bytes and the minimum as 1,024, so the file passes forms that count either way.
Greyscale images: saves the images in shades of grey, which takes less space than colour. Text and drawings keep their colour.

The result shows each file's size before and after, and what was done. View pages shows the compressed PDF one page at a time at 100% zoom, as a PDF reader shows it. The file is named after the original, as in notice-compressed.pdf.

How it works

Most large PDFs are large because of images: a scanned page is a photo of the page, and a phone photo holds far more pixels than a page needs. Text, fonts and drawings take little space in comparison. So the tool works in two steps.

First, the images. The tool reads each page to find how large every image is drawn, which gives its resolution on the page in dots per inch (DPI). An image finer than the level's DPI is scaled down to it, and images are saved again as JPG. An image is replaced only where the new one is smaller, and a JPG is never saved at a higher quality than it already has.

Second, the rest of the file is compressed without loss: its data packed again at the highest setting, small objects grouped together, and fonts or images that no page uses left out. Nothing on the pages changes in this step.

Lossless: the second step only. Nothing on the pages changes: the file is stored more tightly. Scans and photos usually shrink little this way.
Balanced: Images finer than 150 DPI on the page are scaled down to it, and images are saved again as JPG at quality 75 where that makes them smaller. Text and drawings are not changed. At 150 DPI, printed text and handwriting stay sharp on screen and on paper.
Strong: Images finer than 100 DPI on the page are scaled down to it, and images are saved again as JPG at quality 55 where that makes them smaller. Text and drawings are not changed. Smallest, for reading on screen; small print in a scan can soften.
Target size: if lossless compression is already enough, nothing else changes. Otherwise the tool uses one JPG quality and one limit on resolution for every image, so no page looks worse than the rest, and takes the best-looking setting that fits, giving up what shows least first: images are held to 300 DPI, more than a screen or printer shows; then quality falls to 75; then resolution to 150 DPI, which is the Balanced level; then quality to 50; and last, resolution to 72 DPI, below which small print stops being legible.

Some images are left as they are, and the result counts them: black-and-white fax-style scans (CCITT and JBIG2, already very compact), JPEG 2000, CMYK and other print colour spaces, and images in annotations or repeating patterns. A file whose result would not be smaller is kept as it was, and the result says so.

Examples

A phone photo of a page, filling A4

Image: 3,072 × 4,080 px
On the page: 372 DPI
Balanced: 1,240 × 1,754 px at quality 75
Strong: 827 × 1,169 px at quality 55

The photo has about 372 pixels for every inch of the page, more than a screen or printer shows. Balanced keeps 150, so the image has about 17% of its pixels, before the JPG quality saves more.

A portal that takes 50 KB to 200 KB

Compress by: Target size
Max size (KB): 200
Min size (KB): 50
File size: 51.2 KB to 200 KB (51,200 to 200,000 bytes)

The file is at most 200 × 1,000 bytes, and at least 50 × 1,024, so it passes whichever way the portal counts a kilobyte.

Frequently asked questions

A scan is one image a page, and a page of small print needs a certain number of pixels to stay readable. When even the lowest quality and resolution do not fit, the tool says how small it got, and offers to convert the pages to images: each page saved as one JPG at down to 72 DPI. That reaches sizes the original layout cannot, but text can then no longer be selected, and links and form fields are lost. Greyscale images, or splitting the file into parts, are the other ways under a limit.

Yes. Text, fonts, links, bookmarks and form fields are kept; only images are saved again. The one exception is converting pages to images, offered when a size cannot be reached otherwise, which says so before and after.

No. When compressing would not make a file smaller, which happens with PDFs that are already compressed or hold mostly text, the original is kept and the result says so.

Yes. A signature covers the exact bytes of the file, so any change, compression included, makes it no longer verify; the tool says so when you add a signed PDF, such as an e-Aadhaar or a digitally signed certificate. Where a portal checks the signature, upload the original instead.

No. Your browser reads, compresses and saves the files on your device; they are not sent to CornerTools or anyone else, and neither is a password you type. To check, open the browser's developer tools at the Network tab and add a PDF: no request carries it. The PDF engine downloads from this site the first time you use it: a download to your browser, not an upload of your file.