How to Reduce PDF File Size on Mac, Windows, and Mobile (Free)
· 5 min read
Mac Preview has a Reduce File Size filter that is convenient but uncontrollable. Windows has no built-in compressor at all. Phones have none natively. Whatever you use, the outcome depends on what is inside the PDF far more than on the tool: scans shrink enormously, text documents barely shrink at all.
Every platform has its own way of doing this and most of them upload your document to do it. Here is what each option actually costs.
On this page
On a Mac
Preview has a Reduce File Size quartz filter under Export. It is convenient and entirely offline, but it is aggressive and fixed — you cannot control how hard it compresses, and the results on text documents are often poor.
It has a specific failure mode worth knowing about: on a PDF that is already efficient, the filter can produce a file larger than the original, because it re-encodes images that were already well compressed. Always check the output size rather than assuming it went down.
It is worth trying first because it costs nothing. If the output looks bad or barely shrinks, use something with a quality control.
On Windows
Windows has no built-in PDF compressor. Printing to the Microsoft Print to PDF driver sometimes shrinks a file, but it does so by re-rendering, which is unpredictable and can just as easily make it larger.
Microsoft Word can export to PDF with a Minimum size option, which helps if you still have the source document. It does nothing for a PDF you were sent.
Most people end up at a web tool. The thing worth checking is whether it uploads your file, because most do.
Compress PDFCut PDF size for email without wrecking the scanOn a phone
Neither iOS nor Android has a native PDF compressor. App-store options exist but almost all of them upload, and many are aggressive about permissions.
A browser-based tool works on a phone without installing anything. The limit is device memory rather than policy, so very large documents may need a laptop — rendering a hundred pages at once is genuinely demanding on a phone, and the browser will run out of memory before it runs out of patience.
The options side by side
The honest comparison is less about which compresses best and more about what each one costs you in control and privacy.
| Method | Platform | Control | Leaves your device |
|---|---|---|---|
| Preview quartz filter | Mac | None | No |
| Word export at minimum size | Windows, Mac | None | No |
| Adobe Acrobat Pro | Mac, Windows | Full | No, but paid |
| Typical web compressor | Any | Some | Yes — uploaded |
| FileCrisp | Any browser | Three modes | No |
The common thread
Whatever you use, the outcome depends on what is inside the PDF far more than on the tool. Scans shrink enormously. Text documents barely shrink at all, because there is little redundancy to remove.
If a tool claims 90% on a text-only PDF, it is either rasterising it — destroying the text — or overstating what it did.
Working out which kind you have
Open the file and try to select a sentence. If individual words highlight, the document contains real text and its size is font and layout data. If nothing selects, or the whole page highlights as a single block, it is a scan and its size is page images.
That one test predicts your result better than any tool comparison. Scan: expect a large reduction. Text document: expect a small one, and consider splitting instead.
Why the privacy question is not paranoia here
The documents people most often need to shrink are the ones they least want to hand over: signed contracts, bank statements, passports, medical letters, tax returns. Those are precisely the files that arrive as large scans.
A tool that processes in your browser never receives the file at all, which makes the question moot rather than a matter of trusting a policy. It is the reason FileCrisp works the way it does.
Common questions
How do I reduce PDF size on a Mac?
Preview's Reduce File Size filter under Export is built in and offline, but offers no control and occasionally makes files larger. For a predictable result, use a compressor with selectable modes — FileCrisp runs in Safari or Chrome with nothing to install.
How do I compress a PDF on Windows?
Windows has no built-in PDF compressor. If you still have the source document, exporting from Word at minimum size works. Otherwise a browser tool is the practical route, and FileCrisp does it without uploading the file.
How do I reduce PDF size on my phone?
Neither iOS nor Android includes one, and most app-store compressors upload your document. Any modern mobile browser can run FileCrisp instead. Very large documents may exhaust phone memory and are better handled on a laptop.
What is the easiest way to reduce PDF file size?
Open the file in a compressor, pick Balanced, and download. The whole operation takes under a minute. The only real decision is whether you need the text to stay selectable, which rules out the modes that save the most.
Why did my PDF get bigger after compressing it?
Because it was already efficient, and the tool re-encoded content that was previously well compressed. Mac's Preview filter is a common culprit. Nothing is wrong with the file — that document simply has nothing left to remove.
Does reducing PDF size affect print quality?
At 150 dpi, print output on A4 still looks clean. At 110 dpi the softness becomes visible on paper while remaining invisible on screen. Choose based on where the document is going to end up.
Is there a file size limit?
No imposed limit, because there is no server paying for bandwidth. The practical ceiling is your device's memory — a desktop handles far larger documents than a phone.