How to Compress a PDF to Reduce File Size
Choose between basic, strong, and extreme compression levels. See the file size before and after, and download the optimized version instantly.
Introduction
Compress PDF is a free online tool that reduces PDF file sizes while maintaining visual quality. PDF compression is essential when you need to email large PDFs, upload them to websites with size limits, or save storage space. Unlike other PDF compressors that upload your files to remote servers, PDFly compresses your PDF entirely in your browser using client-side JavaScript and WebAssembly. Your file never leaves your device, ensuring complete privacy for sensitive documents. The tool offers three compression levels — Basic, Strong, and Extreme — plus a Target Size mode that compresses to a specific file size. There are no file size limits, no daily usage caps, no watermarks, and no account required. This tutorial covers every compression option, with pro tips for maximum reduction, troubleshooting, and FAQs.
Step-by-Step Guide
Upload Your PDF
Drag and drop your PDF onto the compression workspace, or click to browse and select it.
Choose Compression Level
Select from: "Basic" for light compression, "Strong" for balanced compression, or "Extreme" for maximum size reduction.
Compress and Download
Click "Compress PDF" and see the before/after file sizes. Download the optimized version instantly.
Pro Tips & Best Practices
Use the "Target size" option to compress to a specific file size (e.g., 1MB).
Image-heavy PDFs benefit most from compression.
Scanned PDFs can often be compressed by 80%+ without visible quality loss.
Batch compress multiple PDFs using the Batch Process tool.
Common Use Cases
Email Attachment Optimization
Compress PDFs to fit within the 25MB email attachment limit.
Website Download Speed
Reduce PDF sizes for faster downloads on your website.
Storage Optimization
Compress archival PDFs to save disk space without losing content.
Key Features
Three Compression Levels
Basic, Strong, and Extreme for different needs.
Target Size Mode
Compress to a specific file size like 1MB or 100KB.
Before/After Preview
See file size reduction before downloading.
100% Private
All compression happens in your browser.
Frequently Asked Questions
Basic compression preserves quality almost entirely. Strong and Extreme modes apply progressive downsampling. For most documents, the difference is barely noticeable.
Yes. Use the "Target size" option and the tool iteratively adjusts quality to reach your target.
No. The only constraint is your device's available memory.
Common Issues & Solutions
Compressed PDF quality is too low
Try a lower compression level. Basic compression preserves quality almost entirely. If you used Extreme mode, switch to Strong or Basic. For image-heavy PDFs, try Target Size mode for more control.
File size didn't reduce much
Text-only PDFs are already very small and may not compress much further. Image-heavy PDFs benefit most from compression. Try Extreme mode or use Target Size to force a specific size.
Compression is taking too long
Large PDFs (100MB+) may take 10-30 seconds. Close other browser tabs to free up memory. The process will complete — wait for it to finish.
Target size mode can't reach the target
If your target size is extremely small (e.g., 100KB for a 50MB PDF), the tool may not reach it without severe quality loss. Try a more realistic target or use Extreme mode instead.
Ready to Try Compress PDF?
Put this tutorial into practice right now. Compress PDF is free, browser-based, and requires no signup.
Open Compress PDF