Free Online PDF Compressor
Large PDF files can be slow to email, expensive to store, and frustrating to upload to web forms with size limits. Our free PDF compressor reduces file size by re-saving your document with object stream compression enabled through PDF-Lib. This optimization targets metadata overhead, redundant objects, and structural inefficiencies in the PDF file format.
Upload your PDF, click Optimize, and see an immediate comparison of original versus compressed file sizes before downloading. All processing happens entirely in your browser — your document is never uploaded to any server. For text-heavy PDFs, forms, and documents with structural bloat, compression can produce meaningful size reductions. Image-heavy scanned documents may see smaller savings since image pixel data is already compressed at the source scanner settings.
Many email providers limit attachments to 10–25 MB. Learning management systems, government portals, and job application sites often impose even stricter limits. Compressing a PDF by even 20–30% can mean the difference between a successful upload and a rejected submission.
How to Compress a PDF
- Upload your PDF by clicking or dragging it into the upload area.
- Click Optimize PDF to process the file locally.
- Review the original versus optimized size comparison and percentage saved.
- Click Download to save the compressed file with a
_compressedsuffix.
Who Uses a PDF Compressor?
- Office workers shrink reports and presentations before emailing colleagues.
- Job applicants reduce resume and portfolio PDFs to meet upload size limits.
- Students compress assignment submissions for learning management systems.
- Web developers optimize PDF assets served on websites for faster loading.
- Archivists reduce storage footprint for document collections with structural overhead.
- Anyone hitting email attachment limits make files small enough to send without cloud links.
Key Features
- Object stream compression via PDF-Lib for structural optimization
- Before-and-after file size comparison with savings percentage
- Human-readable file size display in bytes, KB, or MB
- One-click download of the optimized file
- 100% client-side — PDF never leaves your device
- No watermarks or quality degradation on text content
How PDF Compression Works
PDF files contain objects — pages, fonts, images, metadata — stored in a structured format. Over time, exports from different software can leave redundant objects and uncompressed streams in the file. Object stream compression repackages these internals more efficiently without touching the visible content. This is different from image downsampling, which reduces resolution. Our compressor preserves full image quality while optimizing structure, making it a safe first step before trying more aggressive compression methods.
Tips for Better Compression Results
This tool works best on PDFs with text, forms, vector graphics, and metadata overhead. Scanned documents where pages are full-resolution JPEG or PNG images inside the PDF may not shrink significantly because the image data is already compressed. For scanned PDFs, consider scanning at lower DPI or using a dedicated image compression tool first. Always compare the optimized file visually before discarding the original. If the savings percentage is 0% or negative, your PDF was already optimally structured and further compression is not possible with this method. Batch-compress multiple files by processing them one at a time — each run is independent and completes in seconds for typical document sizes. The output file uses a _compressed suffix for easy identification.
Frequently Asked Questions
Why might the file size not decrease?
PDFs consisting mainly of compressed images (like scanned documents) may not reduce in size because the image data is already compressed. This tool focuses on metadata and object stream optimization, not re-encoding images at lower quality.
Is my PDF safe?
Yes. Everything runs locally in your browser. No file is ever uploaded to a server. Your document stays on your device throughout the entire process.
Does compression reduce visual quality?
Object stream compression does not re-encode images or degrade text. The visual appearance of your PDF should be identical to the original. Only the internal file structure is optimized.
How much can I expect to save?
Savings vary widely. Text-heavy PDFs with bloated metadata may shrink 10–40%. Already-optimized files may show 0% savings. Image-heavy scans typically see minimal change. The tool shows exact before-and-after sizes so you can decide whether to keep the optimized version.
Can I compress password-protected PDFs?
The tool attempts to load encrypted PDFs with encryption ignored. Owner-restricted PDFs usually work. PDFs requiring a password to open may fail — use our PDF Unlock tool first.
Should I keep the original after compressing?
Yes, until you verify the optimized file opens correctly and looks identical. If savings are 0% or the compressed file is larger, keep the original. Once confirmed, you can safely delete the larger copy to free disk space.
Is this the same as reducing image DPI?
No. This tool optimizes PDF structure, not image resolution. For significant reductions on scanned documents, you would need a tool that downsamples embedded images — which this compressor does not do, preserving original image quality.