Most email services cap attachments at 10–25MB, but for PDFs you actually want to send and have people easily open, under 5MB is comfortable and under 1MB is ideal. The fastest way to get there: run it through a browser-based PDF compressor — it handles the whole thing locally in about 30 seconds, no upload required.
Quick answer: Drop your PDF into a browser-based compressor, download the smaller version, and check the size. Most PDFs with scanned images compress 50–80%. PDFs that are already mostly text won't shrink much — there's not much to compress.
Why are some PDFs so large?
Before trying to compress, it helps to understand what's making the file large. The main culprits:
Embedded images — By far the most common reason. If someone scanned a document to PDF, each scanned page is a high-resolution image. A 10-page scanned document could easily be 20–30MB if the scanner was set to 300 DPI.
Uncompressed fonts — PDFs embed fonts inside them. Most of the time this is a few kilobytes, but some PDFs embed entire font files.
Duplicate resources — Some PDF creators embed the same image or font multiple times by accident.
No compression settings — Some software (especially older Office versions or certain printers) creates PDFs without optimizing the output.
Multiple merge operations — Merging PDFs together can sometimes inflate the file size if the merger doesn't deduplicate resources.
How to compress a PDF in the browser
The fastest method with no software installation and nothing uploaded to a server:
- Open the PDF compressor in your browser
- Drop your PDF onto it
- Choose a compression level (medium works for most purposes)
- Download the compressed PDF
Check the result size. If it's still too large, try the high compression setting. The quality of text and vector graphics won't be affected — only rasterized images get compressed, and you can control how aggressively.
How to compress a PDF using Adobe Acrobat (if you have it)
If you have Adobe Acrobat (not just Reader):
- File → Save As → Reduced Size PDF — quick compression with minimal settings
- Or File → Compress PDF — gives you size options (reduced, medium, high compression)
- Or File → Save As → Optimized PDF — most control, lets you set image resolution, downsample, remove embedded fonts
The Optimized PDF path is the most powerful. You can set image quality for color images, grayscale images, and black-and-white images separately.
How to compress a PDF using Preview on Mac
Mac's Preview app has a basic PDF compression option:
- Open the PDF in Preview
- File → Export
- Change the Quartz Filter to "Reduce File Size"
- Click Save
This method is a bit aggressive — it can sometimes make images look noticeably worse. Try it on a copy first. For better results, the browser-based approach gives you more control over the quality trade-off.
Targeting specific sizes: what to expect
This varies a lot depending on what's in the PDF:
| PDF type | Starting size | After compression |
|---|---|---|
| Scanned document (300 DPI images) | 15MB | 1–3MB |
| Scanned document (600 DPI images) | 40MB | 2–5MB |
| PDF from Word/Office | 2MB | 500KB–1MB |
| PDF with vector graphics (charts) | 500KB | 400KB (minimal change) |
| Mostly text PDF | 100KB | 80KB (barely changes) |
Text-heavy PDFs don't compress much — the text is already efficiently encoded. Image-heavy PDFs (especially scans) compress dramatically.
I had a 10-year lease agreement that was a scanned document — 28 pages, 34MB. The real estate agent needed it by email but their server bounced attachments over 10MB. I ran it through a browser compressor on medium quality. The result was 4.2MB — under the limit, and the scanned text was still clearly readable. Took about 45 seconds.
What if compression isn't enough?
If the PDF is still too large after compression:
Split the PDF — Send it as multiple smaller files. A 10MB PDF can become two 5MB PDFs with a PDF splitter.
Use a file sharing service — Google Drive, Dropbox, WeTransfer. Share a link instead of attaching the file. This is often cleaner for large documents anyway.
Reduce the source quality — If you're creating a new scan, scan at 150–200 DPI instead of 300. For most reading purposes, 150 DPI is completely sufficient and creates files roughly 4x smaller than 300 DPI.
Remove pages you don't need — If the PDF has appendices or irrelevant pages, extract just the pages that matter with a PDF extractor first, then compress.
Preserving quality while compressing
Compression always involves a trade-off. For text documents and forms that need to be clearly readable:
- Medium compression is usually the right call — reduces size significantly while keeping text crisp
- High compression may make scanned text slightly blurry — test it on a page with fine print
- For photos in the PDF, there's more room for compression before quality degradation is noticeable
Always check the compressed version before sending. Open it, zoom in on a page with small text, and confirm it's still readable at normal zoom levels.
Frequently asked questions
Why is my PDF still large after compression? If the PDF contains mostly text and vector graphics (like a Word document exported to PDF), there's not much to compress — the data is already efficiently encoded. Image compression targets rasterized content like photos and scans. A text-only PDF might only shrink 10–20%.
Is this completely free? Yes — no account, no payment, no watermark needed. You can use it as many times as you want.
Do my files get uploaded to a server? No. The browser-based PDF compressor runs entirely in your browser using WebAssembly. Your files never leave your device.