How to Compress PDF — Reduce File Size Online
Large PDF files can be a headache. They clog up email inboxes, take forever to upload, and eat through storage. With PDFScan Pro, you can compress PDFs online for free — reducing file size while maintaining readable quality. No software to download, no sign-up needed.
When Should You Compress a PDF?
PDF compression is useful in many everyday situations:
- Email attachments — most email providers limit attachments to 25 MB. Compression lets you send large documents without bouncing.
- Web uploads — job applications, government forms, and university portals often have strict file-size limits.
- Storage savings — compressing scanned documents can reduce file sizes by 50-80%, freeing up space on your device or cloud drive.
- Faster sharing — smaller files load and download faster for your recipients.
How to Compress a PDF in 4 Steps
Step 1: Open the Compress PDF Tool
Navigate to the Compress PDF tool. It works on any browser and device — Windows, Mac, Linux, Android, or iOS.
Step 2: Upload Your PDF
Drag and drop your PDF file into the upload area, or click to select it from your files. The free plan supports files up to 25 MB. Pro users can compress files up to 500 MB.
Step 3: Choose Compression Level
Select the compression level that fits your needs. Lower compression preserves higher image quality, while higher compression creates smaller files. For most documents, the recommended (medium) setting offers the best balance.
Step 4: Download the Compressed PDF
Click "Compress" and wait a moment. Once finished, download your smaller PDF file. You will see the before and after file sizes so you know exactly how much space you saved.
How PDF Compression Works
PDF compression reduces file size through several techniques. Images within the PDF are re-encoded at a lower resolution. Duplicate resources like fonts and color profiles are consolidated. Unused metadata and embedded thumbnails are stripped out. The text content itself stays intact — compression mainly targets the images and embedded resources that account for most of a PDF's size.
Tips for Maximum Compression
- Scanned documents compress the most — they are essentially image files, so compression can shrink them by 60-80%.
- Text-heavy PDFs are already small. Compression may only save 10-20%, but every kilobyte counts for email limits.
- Use high compression for documents you only need to read on screen. Use low compression for documents you plan to print.
Frequently Asked Questions
Will compression reduce the quality of my PDF?
Compression primarily affects images within the PDF. Text remains sharp and fully readable. For most screen viewing, you will not notice any difference. If you need print quality, choose the low compression option.
Is online PDF compression safe?
Absolutely. PDFScan Pro processes your files securely. Files uploaded to the server are automatically deleted within 1 hour. We never access or share your documents.
What is the maximum file size I can compress?
Free users can compress files up to 25 MB. Upgrade to Pro for up to 500 MB with priority processing.