PDF Compressor – Compress PDF Files Online Free
PDF Compressor is a free online tool that reduces PDF file size by re-encoding the internal object structure using pdf-lib — entirely in your browser. Upload a PDF, choose a compression level, and download the smaller result. Before and after sizes and the percentage reduction are displayed. Nothing is sent to a server.
Your files never leave your device. All compression is done locally using pdf-lib. No upload, no server, no storage.
Frequently Asked Questions
How does browser-based PDF compression work?
The tool loads your PDF using pdf-lib and re-saves it with useObjectStreams enabled. This re-encodes the internal structure using cross-reference streams, which reduces the overhead of the PDF's object table. Unused objects and redundant metadata are also removed during the save process.
How much can a PDF be reduced in size?
Results vary significantly by PDF content. PDFs that contain many embedded fonts, unoptimized object tables, or redundant metadata can see reductions of 10–40%. PDFs that were already exported from modern tools (Acrobat, Illustrator) with compression enabled may see little or no reduction, in which case the tool shows a "minimal reduction" notice.
Will compression affect the visual quality of my PDF?
The compression applied by pdf-lib is structural — it reorganizes how the file is stored internally but does not re-render or resample images. Visual quality is preserved. The compression levels in the UI refer to the aggressiveness of stream compression, not image downsampling.
Why does "Extreme compression" not reduce size much more than "Low"?
pdf-lib's compression operates on the PDF's object stream encoding, not on embedded image pixels. All four levels use the same structural approach with varying internal parameters. For dramatic image-level compression, dedicated tools that rasterize and resample embedded images are needed — which requires more processing power.
Is my PDF sent to a server?
No. The PDF is read from your device, processed in browser memory using pdf-lib (compiled to WebAssembly), and the compressed result is made available for download via a local object URL. Nothing leaves your browser tab.