How to Reduce PDF File Size on Windows, Mac, iPhone and Android
Every computer and phone can open a PDF, but very few can shrink one. Windows has no built-in PDF compressor at all, the Mac has one hidden in a menu, and phones leave you to find your own way. This guide goes device by device: what's built in, what it does well, where it falls short, and the method that works on all of them.
The short answer
- Mac: Preview's "Reduce File Size" filter works, but it's aggressive and has no settings.
- Windows: nothing built in. Fix the PDF at the source (Word) or use a browser tool.
- iPhone and Android: nothing built in. A browser-based compressor works on both.
First, check what kind of PDF you have
Divide the file size by the number of pages. This quick sum tells you which fix will work:
- Under about 50 KB per page: a text PDF. It's already efficient. A lossless clean-up may trim a third (our 19-page text PDF went from 100 KB to 64 KB), but don't expect miracles.
- Several hundred KB to over 1 MB per page: scanned pages or large photos. These shrink by 70–90%, but only with a method that re-compresses the images.
Our PDF compression test shows both cases with real numbers, including how small a scan can go and still be readable.
On a Mac: Preview
- Open the PDF in Preview.
- Choose File → Export…
- In the Quartz Filter menu, choose Reduce File Size.
- Give the file a new name, so you keep the original, and click Save.
The catch: the filter has no settings. It shrinks every image heavily, which is fine for text documents with a few pictures but often leaves scans blurry and photos blotchy. Some files even come out bigger. If the result looks rough, use the browser method below, which lets you pick a quality level or an exact target size.
On Windows: there's no built-in compressor
Windows can open PDFs in Edge, but neither Edge nor any other built-in app can compress them. You have two good options.
Option 1: fix it at the source in Word
If the PDF came from a Word document you still have, re-export it smaller:
- Shrink the pictures first: click any picture, go to Picture Format → Compress Pictures, untick "Apply only to this picture", and choose a lower resolution such as Web (150 ppi) or E-mail (96 ppi).
- Choose File → Save As, pick PDF as the file type, and set Optimize for to Minimum size (publishing online).
This keeps text sharp and selectable, because only the pictures get smaller. Our guide to reducing Word file size has more fixes.
Option 2: compress the PDF in your browser
If you only have the PDF, or it's a scan, use a browser tool (steps below). It works the same on Windows, Mac, Linux and Chromebook.
On iPhone and iPad
iOS can create PDFs (the Notes app has a document scanner, and in the Files app you can select images and choose Create PDF), but it can't compress them. Two tips:
- Scan smaller to begin with. Scanner apps often default to color. For text documents, switching to grayscale or black-and-white makes much smaller files.
- Compress in Safari. Open compressnfly.com/compress-pdf, tap the upload area, choose Browse to pick the PDF from Files, then save the result back to Files.
On Android
Android has no built-in PDF compressor either. The Google Drive app can scan documents to PDF (tap + → Scan), and like iOS, a browser tool handles compression: open the PDF compressor in Chrome, pick the file from your Downloads or Drive, and download the smaller copy.
On any phone, very long scanned PDFs (dozens of pages) take longer to process than on a computer, because each page is re-drawn on the device. For big jobs, a laptop is faster.
On any device: compress in the browser
- Open the PDF compressor and drop in your file.
- Choose By quality level for a quick result, or To an exact size when a website or email has a hard limit. There are ready-made pages for 200 KB, 500 KB, 1 MB and 2 MB.
- Download the result and open it once to check the smallest text is readable.
Compressnfly runs the compression inside your browser, so the PDF is never uploaded to a server, which matters for contracts, bank statements and ID documents. Most online PDF tools work differently: they upload your file, process it on their servers and send it back.
Which method should you use?
| Situation | Best method |
|---|---|
| You still have the Word file | Compress pictures in Word, export with "Minimum size" |
| Text PDF with a few images, on a Mac | Preview → Reduce File Size |
| Scanned document | Browser compressor with a quality level or target size |
| Upload form with a strict limit | Browser compressor, "To an exact size" |
| Too many pages for the limit | Split the PDF and upload in parts |
| Several PDFs that must be one file | Merge first, then compress |
FAQ
Why did Preview make my PDF bigger?
The Reduce File Size filter re-encodes every image with fixed settings. If the images were already well compressed, re-encoding them can add size. Keep the original and try a different method.
Is there a free PDF compressor for Windows?
Not built in. A browser-based compressor is free and needs no install. If the PDF came from Word, exporting it again with "Minimum size" also works.
Will compressing a PDF remove my signature?
No. A signature image stays on the page. A digital signature (a cryptographic one, shown in a signature panel) is invalidated by any change to the file, though, so compress before signing digitally.
Can I compress a password-protected PDF?
Remove the password first (you'll need to know it), compress, then add protection again if needed.