Compress PDF

How PDF Compression Works

ConvertUnlimited uses pdf-lib and native browser re-encoding to reduce the size of your PDF files. Our tool attempts to rebuild the PDF's internal object structure, removing redundant data and optimizing object streams. For PDFs containing large images, we attempt to downsample the visual data using the browser's graphics engine.

Because all processing is executed on your device's CPU and RAM, selected document contents are processed locally in your browser. This local-first approach provides local browser-based processing and avoids the risks associated with cloud-based compression services.

Why Some PDFs Barely Shrink

PDF compression results vary significantly depending on the document's original structure. Here is why:

• Already Optimized: Many modern PDFs are already saved with maximum compression. In these cases, there is little "slack" to remove.
• Text-Only PDFs: Text takes up very little space. If your 100-page PDF is purely text, its file size is already minimal, and compression will have negligible impact.
• Encrypted Files: Password-protected or encrypted PDFs cannot be re-encoded locally for security reasons, meaning their size cannot be changed.

Text PDFs vs. Scanned PDFs

Scanned PDFs (which are essentially a series of images) compress the most. By reducing the resolution of the scanned layers, we can often shrink the file by 50% or more. Digital PDFs created from Word or Excel are already highly efficient and rarely shrink by more than a few percentage points.

Browser-based PDF Compression Limitations

While cloud tools can use heavy server-side algorithms, browser-based tools must work within the memory and processing limits of your web browser. We focus on "Best Effort" structural optimization that provides the best balance of speed, privacy, and file size reduction without risking a browser crash.

Frequently Asked Questions

Is it safe for sensitive documents?

Yes. Your document stays in your browser's memory. It is not intentionally uploaded by this tool or stored on any disk. You can even use this tool while offline once the page has loaded.

Will my PDF lose quality?

On "Recommended" and "Small File" settings, there may be a minor loss in image clarity, especially on high-resolution scans. Text clarity usually remains identical to the original.

What is the maximum file size?

We don't set a hard limit, but documents over 100MB may exceed your browser's allocated memory during the re-encoding process. If the tab crashes, try using a more powerful device or a smaller file.

Browser Support

This tool works in all modern browsers supporting the File API and WebAssembly, including Chrome, Firefox, Safari, and Edge.