"How do I shrink this PDF?" has one answer with several doorways. The tool that does the work — Compress PDF — runs in a browser tab, so the steps are identical everywhere; what changes by device is how you hand the file over and get it back. This guide walks each platform in turn, then covers the habits that keep documents lean before they ever need shrinking.
The reason a browser tool matters for this question specifically: the traditional alternatives are desktop software to install or upload sites that send your file to a server. A tool that runs entirely in your browser is neither — nothing to install on a locked-down work machine, and nothing uploaded on any machine.
Reduce PDF file size on Windows
Open the tool's page in your usual browser — Edge, Chrome, Firefox, anything current. Drag the PDF from Explorer onto the page, or click to browse for it. Pick a compression level, run it, and the smaller file downloads straight to your Downloads folder.
The part worth noticing on a work computer: there's no installer, no admin prompt, and no license key. If you can open a web page, you can compress the file — which is usually the difference between fixing a document now and filing a helpdesk ticket.
On a Mac
Same steps in Safari or Chrome: drag the PDF from a Finder window onto the page, choose a level, and download. The result lands in your Downloads folder like any other file, ready to attach or file away. Nothing is added to Applications, and nothing keeps running once you close the tab.
On iPhone or iPad
Open the page in Safari or your preferred browser. Tap the upload area and the Files picker appears — browse to wherever the PDF lives, whether that's iCloud Drive, On My iPhone, or another cloud provider's folder. After processing, the compressed copy saves back through the Files app, and from there you can share it straight into Mail or Messages.
Files up to 100 MB are supported — more than phone cameras and scanner apps produce in normal use, so the document you're holding will fit.
On Android
Open the page in Chrome. Tap upload, and the Android file picker lets you choose the PDF from Downloads, Files, or your cloud storage. The compressed copy comes down through the browser's normal download flow — notification shade, Downloads app — ready to attach from any app that asks for a file.
Choosing a level on any device
Three levels, one question: how much image quality can this document afford to trade?
- Low strips metadata and optimizes structure only — images stay exactly as they were. Right for text documents, or any file whose images must not change.
- Medium recompresses images at a balanced quality — the sensible default for documents people will read on screen.
- High uses a lower image quality and produces the smallest possible file — for when the document simply must fit somewhere tight.
DPI and grayscale options live under Advanced and apply at Medium and High. The trade-off at those levels is real but invisible at reading size: images are re-encoded to match the size they actually display at. Keep a copy of the original whenever the images might later be printed large or inspected closely.
Keep files lean at the source
Compression is a rescue operation; the cheaper fix is not needing it. Two habits in Word and Google Docs prevent most oversized exports. First, resize images before inserting them — a photo is typically embedded essentially in full, so a five-megapixel original becomes five megabytes of PDF even when it displays at postage-stamp size. Second, use your word processor's smaller-file export option where one is offered — many PDF export dialogs include a "minimum size" style choice, and it's the right one for documents headed for email rather than print.
In Google Docs the same logic applies: shrink the images inside the document, then download as PDF. The exported file can only be as lean as what went into it.
How small will it actually get?
Honestly: it depends entirely on what's inside. A scan or a photo-heavy brochure can shrink dramatically, because its weight is images that can be re-encoded. A text-only document barely moves — its content is already tiny, so Low's tidy-up is all there is to gain. And a document that's large because it genuinely contains a hundred dense pages will stay large; compression trades image detail for bytes, and it won't invent space that isn't there.
The thirty-second check before you attach
Compression reports the result's size when it finishes — that number is the whole point of the operation, so look at it before you do anything else. Compare it against the limit you're aiming at (remembering that email encoding adds roughly a third in transit, so a 25 MB cap means a file under about 18 MB). Then open the compressed copy and scroll it once, at normal reading size. You're not proofreading — you're confirming the trade you knowingly made: text untouched, images fine at reading distance. Ten seconds of scrolling, and you can attach the file with a clear conscience.
When smaller still isn't small enough
Some files stay over the line even at High — usually long scans, where every page is an image and the content genuinely weighs that much. At that point the levers left are structural: split the document into parts that each fit, or share a link instead of an attachment. The full decision — compress, split, or link, and in what order — is laid out in How to Send a Large PDF by Email, and the diagnostic side (what's normal, what's too big, and why) lives in the PDF File Size Guide.
That's the whole method — the same page on every device, a level matched to the content, and lean habits at the source so the rescue operation stays rare.