Compress PDF
Reduce PDF file size locally in your browser. Your files stay on your device.
Local-first PDF compression
Make documents smaller, faster.
Drag in your PDF. Our tool optimizes the internal structure to reduce file size while maintaining readability. No uploads, no server processing.
Processing happens in your browser. Files are not uploaded.
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, your sensitive documents never leave your machine. This local-first approach provides 100% privacy 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 never uploaded to our servers 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.
Privacy Policy
Your Documents: We do not collect, store, or transmit any PDF files. All processing is strictly local.
Analytics: We use Google Analytics 4 to monitor site traffic. This data is anonymized and does not include document content.
Advertising: We use Google AdSense to display ads. These partners may use cookies to serve relevant ads based on your visit to this and other sites.
Terms of Use
ConvertUnlimited is provided "as is" without warranty of any kind. You are responsible for the content you process and must ensure you have the legal right to compress the documents you provide. We are not liable for any data loss or system performance issues resulting from the use of this tool.