How PDF compression works here
Compress PDF resaves the source PDF in the browser using object streams so the file may become easier to share. It is a safe local optimization step, not an image recompression or quality-reduction service. Some already optimized PDFs may not become smaller.
What to expect from the result
After processing, 100PDF shows the original and output sizes so you can confirm whether the file actually changed. If the downloaded file is not smaller, the PDF likely had little removable overhead. Keep the original file and decide whether the new copy is useful for your workflow.
Privacy and limits
The PDF is handled locally in your browser and is not sent to a 100PDF server for compression. This tool does not perform OCR, repair broken PDFs, downsample embedded images, or convert Office files. Very large or malformed PDFs may fail depending on browser memory.