How to Compress a PDF: Online, iPhone, Mac, Windows and Android
Shrink a PDF for email or an upload limit. Clear steps for the browser, iPhone, Mac Preview, Windows and Android, plus why some PDFs barely get smaller.
By Awais, Founder and editor-in-chiefPublished
To compress a PDF, open it in a PDF compressor, choose how strongly to compress it, and save the smaller copy. The quickest way on any device is a browser tool such as our free Compress PDF, and Macs and iPhones also have a built-in option in Apple’s Preview app.
This guide gives the exact steps for each device, the size limits you are most likely to hit, and what to do when a file refuses to shrink.
What makes a PDF large
A PDF is a container. Text and vector drawings take up very little space. Photos and scanned pages take up a lot. That is why a 40-page report saved from Word can be a few hundred KB, while a scan of the same pages can run to 10 MB or more.
Here is the maths for one scanned page. An A4 page scanned at 300 dpi is 2,480 × 3,508 pixels, or about 8.7 million pixels. Stored in full colour with no compression, that is about 26 MB for a single page. Scanners compress it, but a page can still weigh a megabyte or more. Scan the same page at 150 dpi and you get 1,240 × 1,754 pixels: exactly a quarter of the pixels.
That is the main trick behind PDF compression. A compressor mostly works on the images inside the file:
| Technique | What it does | Where it helps most |
|---|---|---|
| Downsampling | Lowers image resolution, for example from 300 to 150 dpi | Scans and photo-heavy files |
| Recompressing | Saves images again as JPEG at a lower quality | Photos, brochures, slide decks |
| Grayscale | Drops colour from images | Scanned letters and forms |
| Clean-up | Removes duplicate fonts, thumbnails, metadata and unused objects | Files edited many times |
If a PDF is almost all text, there is little for a compressor to remove. More on that below.
How to compress a PDF online (any device)
A browser tool works the same way on a phone, tablet or computer.
- Open Compress PDF in Chrome, Safari, Edge or Firefox.
- Choose your PDF, or drag it onto the page.
- Pick a compression setting. A stronger setting gives a smaller file but softer images.
- Download the result and open it. Zoom in on small print, stamps and signatures to make sure they are still clear.
Our tool compresses the file inside your browser, so the PDF is not uploaded to a server. That matters for bank statements, payslips, contracts and ID scans, which you should not hand to a website you don’t know.
How to compress a PDF on iPhone and iPad
You have two options.
Use a browser tool in Safari. Open the compressor, tap to choose a file, then tap Browse to pick the PDF from the Files app, iCloud Drive or another storage app. Safari saves the smaller copy to the Downloads folder in Files, where you can share it to Mail or WhatsApp.
Use Apple’s Preview app (iOS 26 and later). Apple added Preview to iPhone and iPad, and it can export a smaller copy of a PDF. Open the PDF in Preview, tap the menu next to the file name, choose Export, and use the file size slider before you save. Apple describes this in its guide to exporting or compressing PDFs in Preview on iPhone. For a full walkthrough and troubleshooting, see how to compress a PDF on iPhone or iPad.
How to compress a PDF on a Mac with Preview
Preview has a built-in filter called Reduce File Size.
- Open the PDF in Preview.
- Choose File > Export.
- Open the Quartz Filter pop-up menu and choose Reduce File Size.
- Type a new name so you keep the original, then click Save.
Apple warns that the compressed PDF may be of lower quality than the original (Apple Support). The filter can shrink images hard, so check scanned text before you send it. On macOS Tahoe 26 and later, the Export dialog also has checkboxes such as Optimize images for screen and Save images as JPEG. Try those if the filter makes text too blurry, or use a browser tool where you can choose a lighter setting.
How to compress a PDF on Windows
Windows 11 does not include a PDF compressor. Microsoft Edge, the default PDF viewer, can open, annotate and print PDFs, but it has no option to make them smaller. A browser tool is the simplest fix:
- Open Edge or Chrome and go to Compress PDF.
- Click to choose the file, or drag it from File Explorer onto the page.
- Pick a setting and download the result. It lands in your Downloads folder.
If you created the PDF yourself in Microsoft Office, fix the size at the source. When you save as PDF from Excel or PowerPoint, Microsoft offers a Minimum size (publishing online) option (Microsoft Support). In Word, select a large picture, use Picture Format > Compress Pictures to lower its resolution, and then save as PDF.
Zipping a PDF rarely helps. The images inside are usually already compressed, so a ZIP file ends up only slightly smaller.
How to compress a PDF on Android
Android has no built-in PDF compressor either. The compress option in Files by Google creates ZIP archives, which barely shrink PDFs.
- Open Chrome and go to Compress PDF.
- Tap to choose a file, then pick the PDF from Downloads, Google Drive or another app in the file picker.
- Choose a setting and download the result. It is saved to your Downloads folder.
More detail, including WhatsApp and Gmail limits, is in how to compress a PDF on Android.
Size limits you are likely to meet
Most people compress a PDF to get under one of these limits:
| Where | Limit | What happens with bigger files |
|---|---|---|
| Gmail (personal accounts) | 25 MB | Gmail swaps the attachment for a Google Drive link |
| Outlook.com | 25 MB per file | OneDrive links allow up to 2 GB |
| Yahoo Mail | 25 MB for all attachments | The message can’t be sent |
| iCloud Mail | 20 MB per message | Mail Drop handles up to 5 GB |
| USCIS online filing | 12 MB per file | The upload is refused; PDF, JPG or JPEG only |
Two things catch people out. First, email attachments are encoded for sending, which adds roughly a third to their size, and some services count that encoded size. Leave a margin. Second, application portals for jobs, exams, visas and universities often set their own caps per file, and some are far below email limits. The rule is usually printed next to the upload button or in the instructions PDF. USCIS, for example, also asks you not to password-protect uploads and to make sure every page is readable.
How to get under a strict limit
If one pass of compression is not enough, work through these steps in order:
- Use a stronger setting. Then check the result at 100% zoom.
- Remove pages you don’t need. Blank backs of scanned pages and duplicate copies add weight. Delete PDF Pages takes them out.
- Split the file. If the portal accepts several uploads, Split PDF can cut one large file into parts that each fit the limit.
- Rescan at a lower resolution. For text documents, 150 to 200 dpi in grayscale is usually readable. Each step down from 300 dpi to 150 dpi removes three quarters of the pixels.
- Shrink photos before you make the PDF. If you are building a PDF from phone photos, reduce the photos first, then combine them.
A rough example: a 12-page bank statement scanned in colour at 300 dpi, at about 1.5 MB per page, comes to around 18 MB. That is too big for most email services once encoding is added. Rescanned at 150 dpi, each page has a quarter of the pixels, so the image data shrinks to roughly a quarter as well, before any extra compression.
What compression can’t do
Compression can’t make a text-only PDF much smaller, because text is already stored efficiently. It also can’t fix a scan that is blurry to begin with: compressing a poor scan only makes it worse. If you need to combine several compressed files into one, see how to merge PDF files, and compress once more at the end if the combined file is too big.
FAQ
Does compressing a PDF reduce quality?
It can. Compression mostly works on images, so photos and scans may look softer, while normal text and vector graphics stay sharp. Always zoom in on small print before you send the file.
Why did my PDF barely get smaller?
It is probably mostly text, or its images are already well compressed. Try removing unneeded pages or splitting the file instead, as described in how to split a PDF.
Is it safe to compress a confidential PDF online?
It depends on the tool. Many websites upload your file to their servers. Our Compress PDF tool works inside your browser, so the document stays on your device.
Can I compress a password-protected PDF?
Usually only after the protection is removed, because the tool has to open the file to change it. If a PDF asks for a password when you open it, you need that password first.
How do I get a PDF under 1 MB?
Use a strong setting, delete pages you don’t need, and for scans use 150 dpi grayscale. If it is still too big and the form allows several files, split it into parts.