How to Compress PDF Files Online
Choose how much image detail to keep, then review the finished size and pages before downloading your PDF.
Add Your PDF Files
Select one PDF or add several files to compress in the same batch. Enter the correct password when a protected document asks for it.
Choose a Compression Level
Select Lossless, Low, Recommended, High, or Maximum compression. Recommended is selected by default for a practical balance between file size and image quality.
Compress, Review, and Download
Compare the original and finished sizes, preview the result, then download one compressed PDF or all completed files together as a ZIP.
How Does the CompressFly PDF Compressor Work?
Every preset rewrites and compresses the PDF structure. Lossless compression leaves embedded images unchanged, while Low, Recommended, High, and Maximum progressively reduce their resolution and encoding quality. Existing text stays selectable because pages are not flattened into images. If compression would create a larger file, the original is kept. Each PDF is processed locally in your browser, whether you add one file or several.
What "processed locally" means
- PDF files are not uploaded to or stored on a processing server
- Compression runs on your device inside the browser tab
- Passwords used to open protected PDFs are handled on your device
- Multiple PDFs are processed separately and remain separate outputs
Choose the Right PDF Compression Level
Start with Recommended for everyday use, move toward Lossless when image detail matters, or choose a stronger level when reducing file size matters more.
| Compression level | What it changes | Best for |
|---|---|---|
| Lossless | Keeps original image data and compresses the PDF structure | Documents where image quality must not change |
| Low compression | Caps embedded images at 300 DPI with a quality setting of 85 | Detailed graphics, print copies, and lighter size reduction |
| Recommended | Caps embedded images at 150 DPI with a quality setting of 75 | Email, web delivery, and routine document sharing |
| High compression | Caps embedded images at 96 DPI with a quality setting of 60 | Smaller copies intended mainly for screen reading |
| Maximum compression | Caps embedded images at 72 DPI with a quality setting of 45 | When file size matters more than fine image detail |
Results depend on the PDF’s contents. Scans and image-heavy documents usually have more data to reduce, while text-only or already optimized PDFs may become only slightly smaller. Quality settings are encoder values, not promised percentages of visual quality or file-size reduction.
Why Use CompressFly to Compress PDF Files Online?
Easy to Use
Make a PDF easier to send without learning a document-optimization application. The focused compressor keeps an everyday file-size task straightforward.
Easier Document Sharing
Smaller PDFs can be more convenient for email attachments and online submissions. You can prepare a lighter working copy while keeping the source document available.
Clear Results
The finished size and document preview help you judge whether the copy suits your needs. You can make an informed choice instead of assuming every compression result is useful.
No Installation Required
Reduce the file size directly in your browser without setting up desktop software. A large attachment does not need a full PDF editing suite.
Free Without an Account
Compress your documents without buying a subscription or registering. There is no payment step before you can download the result.
Private Local Processing
Your PDF does not have to leave your device to be compressed. Documents and passwords are handled in the browser rather than uploaded to a processing server.
PDF Compression FAQ
How do I compress a PDF online?
Compress PDF files in three steps: 1. Select one PDF or add several files. 2. Choose Lossless, Low, Recommended, High, or Maximum compression. 3. Click “Compress PDF,” review the result, then download one PDF or the completed batch as a ZIP.
Which PDF compression level should I choose?
Recommended is the practical default for email, web delivery, and everyday sharing. Choose Lossless when image quality must stay unchanged, Low for lighter image compression, or High and Maximum when a smaller file matters more than fine image detail.
Does PDF compression reduce image quality?
Lossless compression leaves embedded images unchanged. Low, Recommended, High, and Maximum re-encode images at progressively lower resolution and quality settings, so stronger levels can soften photographs and scanned pages. Preview the finished PDF before sharing it.
Can I compress several PDFs at once?
Yes. Add multiple PDFs and the selected compression level is applied to each file separately. Review individual results, download files one by one, or download the completed batch as a ZIP.
Can I compress a password-protected PDF?
Yes, when you know the correct password. The PDF and password are handled locally in your browser so the document can be opened and compressed on your device.
Can I compress a PDF to an exact file size?
This page controls compression strength rather than the final number of kilobytes. For a preset size requirement, use Compress PDF to 100 KB, Compress PDF to 500 KB, or Compress PDF to 1 MB.
Why is my compressed PDF only slightly smaller?
Text, vector artwork, fonts, and already optimized images may leave little data to reduce. If the compressed output would be larger than the original, the tool keeps the original file instead.