PDFStack Tool
Compress PDF — Reduce File Size Free Online
Shrink oversized PDF files for email attachments, web uploads, or storage without sacrificing readability. PDFStack compresses PDFs client-side using object stream optimization — a lossless technique that strips redundant internal data.
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No file uploads
No account required
Free to use
Private & secure
Why compress PDFs with PDFStack?
Email providers cap attachments at 10–25 MB. Cloud storage fills up fast. PDFStack's compression uses object stream packing to restructure the PDF's internal binary representation, often reducing file size by 10–40% without re-encoding images or degrading text quality. And because it runs in your browser, confidential documents never touch a third-party server.
How to compress a PDF
- 1Select Compress PDF in PDFStack.
- 2Upload your PDF.
- 3Click Compress — PDFStack will show you the exact percentage and KB saved.
- 4Download your smaller PDF instantly.
All processing happens locally in your browser — no files are uploaded to any server.
Common Uses
Compress PDFs before emailing contracts, uploading to HR portals, sharing on Slack, or archiving to cloud storage. Especially effective on PDFs exported from Microsoft Word or macOS Preview which tend to carry bloated metadata.
Frequently Asked Questions
How much will my PDF shrink?
It depends on the source. PDFs with lots of redundant metadata or unoptimized streams can shrink 20–40%. Already-optimized PDFs may see smaller gains.
Will compression reduce quality?
PDFStack uses lossless object-stream compression, so text sharpness and image quality are preserved.
Does it work on password-protected PDFs?
You'll need to unlock the PDF first using the Unlock PDF tool, then compress it.
Is there a size limit?
No server limit. The only constraint is your browser's available memory.