The short answer
To reduce PDF file size on any computer or phone, open Reduce PDF size in your browser, add the PDF, keep the Balanced level and download the smaller copy. The file is processed on your own device and never uploaded (here is how to check that a tool does not upload), there is no account and no watermark.
Reduce PDF SizeDrop your PDF, keep Balanced, and download a smaller copy.Open itIf a form or email system has a hard limit, switch on the option to stay under a file size and enter the number, or open the page made for your limit: 1 MB, 2 MB, 500 KB, 200 KB or 100 KB. The rest of this guide explains why that works and what to do when it does not.
Why a PDF is big in the first place
Before you shrink anything, it helps to know where the size comes from. A PDF of pure text is small whatever its length: a 300 page report with no pictures can be a few hundred kilobytes. A PDF over a few megabytes is nearly always big because of pictures:
- Scanned pages. Every page is a photograph of paper, often at 300 dpi or more.
- Photos. A phone photo of 4000 by 3000 pixels placed in a small corner of a page still carries all its pixels.
- Slides with oversized pictures. A deck exported from a presentation app can hold a few huge images that are displayed small.
That is the lever. Compression here means recompressing those pictures at the size they are actually shown, and packing the rest of the file more tightly. Text, fonts, links, bookmarks and form fields are not touched, so text stays selectable and searchable. This is different from tools that flatten each page into one picture to get a small number, which ruins text.
Compress a PDF on a Mac
Mac has a built-in option in Preview: open the PDF, choose File, then Export, and set Quartz Filter to Reduce File Size. It is quick and needs no downloads, but it is a blunt tool. The built-in filter tends to make pictures noticeably soft and gives you no say over the result, and it sometimes produces a file that is barely smaller or even larger. It also cannot aim for a particular size.
A browser tool gives you control. In Safari or Chrome on macOS, open the page, drop the PDF on it, choose a level and, if you need a specific number, a size to stay under. Compare the before and after sizes, then download. If the result is not noticeably smaller, you get your original back and the page says so, so you never end up with something worse than you started with.
Compress a PDF on Windows
Windows has no built-in PDF compressor. Printing to Microsoft Print to PDF sometimes shrinks a file, but it often rebuilds pages in odd ways, loses links and bookmarks, and can make some files bigger. Heavy desktop PDF software does the job but is rarely free.
In Edge, Chrome or Firefox, the browser method is identical to the Mac one: open the page, choose the PDF in the file dialog or drag it in, pick a level, and save the result. Because there is no upload, a 40 MB scan does not wait on your internet connection either.
Compress a PDF on iPhone or Android
The same page works in a phone browser. Tap to choose the file from Files, iCloud Drive or Google Drive, run it, and save the smaller copy back to your phone. Phones have less memory than computers, so a very large PDF is the one place you may hit a limit. If the browser stops, nothing is lost: try again on a computer, or split the document first with Split PDF into pages and compress the parts. The guide to splitting a PDF into pages shows how.
Choosing a level
There are three levels, and one question decides which: where will this file be read?
- High quality keeps pictures up to 220 dpi. Use it when the PDF will be printed.
- Balanced keeps pictures up to 150 dpi. This is sharp on screens and right for email, and it is the default.
- Smallest keeps pictures up to 110 dpi. Use it when size matters more than detail.
In our tests, a PDF of six full page photos went from 4.8 MB to 1.4 MB at Balanced, a colour scan from 1.1 MB to 422 KB, and a deck of five slides with oversized pictures from 38 MB to 184 KB. Your files will differ, and a PDF that is mostly text may barely change.
Getting under a size limit
Portals love round numbers. When you give the tool a limit, it starts at your chosen level, and only if the file is still too big does it look for the highest picture resolution at which the file fits, then recompress the pictures at that size. You never get more shrinking than the limit needs.
- 2 MB is generous. Readable scans and sharp pictures fit, and it suits email and e-signature services.
- 1 MB suits tickets, portals and email. Most documents can meet it and stay clear.
- 500 KB is for scans and documents with a few pictures.
- 200 KB is the usual limit on application portals for CVs, certificates and ID scans.
- 100 KB is for forms with a very small limit and works best for text pages with a few small pictures.
The limits are counted in thousands of bytes (1 MB is 1,000,000 bytes), the smaller way of counting, so the file is under the limit however a form measures it. If the number cannot be reached, you get the smallest result the tool could make, and it tells you how far over you are. Honest failure beats a broken file.
What compression cannot do
- It cannot open password protected PDFs, and it does not remove passwords.
- A digital signature is no longer valid on a compressed copy, because the file has changed. Compress before signing, not after.
- A file that claims PDF/A may stop meeting it.
- A PDF that is mostly text, or one whose pictures are already small, has little to give.
If you have a signed or archived PDF, keep the original and treat the compressed copy as a convenience version for sending.
Other ways to make a PDF lighter
Compression is not the only lever. If the PDF has pages you do not need, removing them shrinks the file directly and is lossless. If you built the PDF from photos, make it again with the Smaller file setting on JPG to PDF. And if you want to strip the title, author and other hidden information at the same time, Remove PDF metadata handles that. The guide to deleting pages from a PDF covers the first idea, and what your PDF reveals about you covers the last. For a single photo with its own size limit, see how to reduce a photo to 200 KB or less.
When you send a file by email, remember that attachments are encoded for transport and grow by about a third. A 7 MB PDF can fail against a 10 MB limit for that reason, so aim for a margin. If you are joining files too, merge first and compress last, as the guide to combining PDF files suggests.