How to Compress a PDF Without Losing Quality
Large PDFs are a persistent headache. Email servers reject attachments over 10–25 MB, cloud storage fills up fast, and sharing a 50 MB document over a messaging app is awkward for everyone. Compressing a PDF is the obvious fix — but most guides either point you toward expensive desktop software or online tools that upload your files to a third-party server.
This guide shows you how to compress a PDF for free, in your browser, without sending your file anywhere.
Why are PDFs so large?
PDFs grow large for a few main reasons:
- High-resolution embedded images — photos or scans at 300+ DPI add significant weight
- Multiple embedded fonts — a PDF embeds font files so it renders correctly on any machine
- Scanned documents — a scanned page is essentially a full-resolution image, repeated for every page
- Uncompressed page content — some PDF exporters don't apply compression to vector or image layers
The most effective way to reduce file size is to re-encode embedded images at a lower resolution or JPEG quality level. This typically cuts file size by 50–80% for image-heavy documents.
Quality vs. size: which setting should you choose?
Before compressing, think about what the PDF is for. The right quality level depends on the end use:
| Use case | Recommended DPI | File size impact |
|---|---|---|
| Email, web, screen reading | 72–96 DPI | Smallest |
| Office presentations, sharing | 100–150 DPI | Medium |
| Standard printing | 150–200 DPI | Moderate |
| High-quality print output | 300 DPI | Larger |
For most day-to-day tasks — emailing a form, sharing a report, uploading to a portal — Medium quality (around 86 DPI) is the right choice. It looks sharp on any screen and keeps file size manageable.
How to compress a PDF in your browser
Most online PDF compressors upload your document to a remote server. That means your contracts, medical records, or financial reports pass through infrastructure you have no visibility into. Browser-based processing avoids this entirely.
Compress PDF free — files never leave your device
Open Compress Tool →Here's how to use the PeakPDFs compressor:
- Go to the Compress PDF tool
- Drag your PDF onto the drop zone, or click to browse
- Choose a quality level:
- Low — 58 DPI, JPEG 50% — smallest file, good for archiving or screen-only use
- Medium — 86 DPI, JPEG 75% — balanced for most purposes (recommended)
- High — 126 DPI, JPEG 92% — best quality, still meaningfully smaller than the original
- Click Compress PDF
- Download the smaller file instantly
How much smaller will it get?
Results depend heavily on the content type:
- Scanned documents and image-heavy PDFs: typically 60–80% smaller
- Mixed content (text + images): typically 40–60% smaller
- Text-only or vector PDFs: typically 20–40% smaller
One important limitation
Browser-based compression works by rasterising each page to a JPEG image and rebuilding the PDF around those images. This means text won't be selectable or searchable in the output file. Page layout, margins, and visual appearance are preserved, but the underlying text layer is lost.
For most everyday uses — emailing a scan, reducing a portfolio, sharing a form — this is a non-issue. But if you need the output to remain searchable or editable, use the High quality setting to minimise visual degradation, or consider a desktop tool like Adobe Acrobat's "Reduce File Size" feature, which applies smarter compression that preserves text layers.
Frequently asked questions
Does compressing a PDF damage the file permanently?
Compression is lossy — the original file size cannot be recovered from the compressed version. Always keep a copy of the original before compressing if you might need the full resolution later.
What's a good PDF file size for email?
Most email servers cap attachments at 10–25 MB. Aim for under 5 MB for reliable delivery across all providers. If you have a multi-page scanned document, Medium compression usually gets it there.
Can I compress a PDF for free without signing up?
Yes. PeakPDFs requires no account and is completely free. Your file never leaves your device.
Will the compressed PDF look different?
At Medium or High quality, the difference is barely visible on screen. At Low quality, images will look slightly softer — still readable, but not print-sharp. Text rendered as vector (not scanned) stays crisp regardless of quality setting.
My PDF is still too large after compressing. What can I do?
Try the Low quality setting first. If it's still too large, the PDF may contain a very high number of pages or very large scans. Consider splitting it into smaller chunks using the Split PDF tool, then compressing each part separately.