How to make a PDF smaller: compress it step by step

Drop the PDF anywhere on the page, or press Add files. You see its pages in the middle, and its size in the file list. A Word, Excel or PowerPoint file or a photo can go in too - it is turned into a PDF as it arrives, then compressed like any other.

The three levels decide how far the pictures in the file are scaled down; everything else is done the same way at every level.

• Light - barely visible quality loss. Photos are kept at about 220 dpi on the page, enough to print them as photos. Choose it when the pages still have to look pristine.
• Balanced - the usual choice. About 150 dpi: clearly smaller, still fine on any screen and on an office printer.
• Strong - the smallest file. About 100 dpi: photos get noticeably softer, which is fine for e-mail and archiving.

The resolution is judged at the size a picture is printed on the page, not by its pixel count: a small logo made of many pixels is reduced, a full-page photo that is already modest is left alone. A picture is only touched when it is clearly over the target.

• Pictures are scaled down to the level's resolution and saved again as JPEG. Transparent parts stay transparent.
• Fonts that are embedded several times - Word does this for every header and footer - are folded into one copy. This changes nothing on the page.
• Page content is tidied: drawing coordinates written with absurd precision are rounded, which on a magazine page alone is worth a fifth of its vector content.
• The file structure is rewritten in a more compact form.

Text and vector drawings are rewritten without loss: they stay sharp at any zoom, and the text can still be selected, copied and searched. Links, bookmarks and form fields survive.

Each step is only kept if it really made the file smaller. A file that can't be made smaller is not made worse.

Press Compress PDF. A large file can take a little while - the button counts the pictures as it goes. When it is done, the smaller file is saved to your device at once, and the file list shows the size before and after, with the percentage saved.

The button says Saved, then turns into Save after a few seconds: press it to save the same file again if your browser held the first download back. Choosing another level turns it back into Compress PDF, so you can try Strong after Balanced and keep the one you like.

You can add several files and compress them all in one run - two at a time without an account or with a free one, any number with Pro; more than one result is saved as a single ZIP. Above the file list, Apply to decides how the level is set:

• Selected file - the level you pick belongs to the file selected in the list. Each file can have its own: a brochure on Strong, a contract on Light. A file with its own setting wears an own badge.
• All files - one level for every file. The files' own settings are set aside, not lost: switch back to Selected file and they apply again.

Under Selected file, Copy to the other files under the options gives the level you see to every other file as its own - a quick start you can then adjust file by file.

When there is nothing left to take off, the tool says Already compressed and saves nothing for that file - handing back the same bytes under a new name would only look like something happened. This is usual for:

• a file that was compressed before, by us or by another program;
• a scan already saved at a low resolution.

A document made only of text and vector drawing - a contract, an invoice exported from an office program - has no photos to shrink either: expect a few percent at most, from the tidier structure and the folded fonts.

If you want to know what makes a file big before you try, Inspect PDF breaks its size down: pictures, fonts, page content. A colour scan that only needs to be readable can also go through Convert PDF to grayscale first.

Without an account, and with a free one, you can compress two files at a time, up to 25 MB each. With Pro there is no size or file-count limit. However big the file, it is compressed on your own machine - which is also why a very large file takes as long as your computer needs for it.

• Need to send only part of it? Split PDF or Extract Pages first, then compress the part.
• The file will be read on a website? Linearize PDF makes the first page appear while the rest is still downloading - run it last.
• Pages of different sizes? Resize PDF pages puts them all on A4.