liminfoPDF Compress
Free web tool: PDF Compress
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About PDF Compress
The PDF Compressor reduces PDF file sizes by creating a clean copy of the document using the pdf-lib library, entirely within your browser. The compression technique works by loading the original PDF, creating a brand new empty PDF document, and then copying all pages from the source PDF into the new document. This process strips out unused objects, redundant cross-reference tables, deleted content that was not properly removed, and other bloat that accumulates in PDFs that have been edited multiple times.
Office workers, students, developers, and anyone who regularly sends PDFs by email or uploads them to size-limited portals will benefit from this tool. PDFs created by exporting from Word, PowerPoint, or other editors often contain hidden unused data that can significantly increase file size. Re-saving through pdf-lib removes this overhead. The tool also copies title, author, and subject metadata from the original to the compressed output.
Choose from three compression levels: Low Compression (High Quality) preserves maximum fidelity and is ideal for print, reducing file size by roughly 5–30%. Medium (Balanced) enables object stream compression for a 20–50% reduction — perfect for email and general sharing. High Compression (Smaller Size) maximises object-stream packing to achieve 30–70% reductions, best for web upload and mobile use. All processing runs 100% in your browser — your PDF never leaves your device.
Key Features
- Three compression levels: Low (High Quality, 5–30%), Medium (Balanced, 20–50%), High (Smaller Size, 30–70%)
- Reduces PDF file size by stripping unused objects and redundant data using pdf-lib
- Creates a clean new PDF by copying all pages, removing hidden deleted content
- Copies title, author, and subject metadata from the original to the compressed PDF
- Visual before/after progress bar showing exact file size reduction percentage
- Supports PDFs with the ignoreEncryption option — handles some restricted PDFs
- Output file named with "_compressed" suffix for easy identification
- Supports PDF files up to 50 MB — 100% client-side, no server upload
- Dark mode support and responsive layout for use on any device
Frequently Asked Questions
How does the PDF compression work technically?
The tool uses pdf-lib to load the original PDF, create a new empty PDF document, and copy all pages from the original into the new document using copyPages(). This process discards any objects that are not referenced by the page tree — including deleted images, outdated content streams, unused fonts, and bloated cross-reference data — resulting in a smaller, cleaner PDF. The High and Medium levels also enable useObjectStreams, which packs indirect objects into compressed object streams for additional size savings.
What is the difference between the three compression levels?
Low (High Quality) rebuilds the PDF structure without object streams, removing unused objects while keeping maximum compatibility and image fidelity — suitable for print. Medium (Balanced) adds object-stream compression which reduces cross-reference overhead and typically achieves 20–50% reduction. High (Smaller Size) uses the same object streams but with tighter settings and is best for web uploads and mobile. None of the levels re-encode or downsample embedded images; they operate purely on PDF structure.
Will this compress images inside the PDF?
No. This tool performs structural compression by removing unused objects and rebuilding the PDF document graph. It does not re-encode or down-sample embedded images. If your PDF is large primarily because of high-resolution images, the size reduction may be minimal. For image re-encoding, you would need a dedicated tool such as Ghostscript or Adobe Acrobat.
How much can I expect the file size to decrease?
Low compression: 5–30%. Medium: 20–50%. High: 30–70%. The actual reduction depends on how much unused data is in the original PDF. PDFs edited and saved multiple times (e.g. Word exports edited in Acrobat) tend to have significant bloat. Clean PDFs generated directly for distribution may see little change regardless of the compression level.
Does the tool preserve the PDF's content and formatting?
Yes. The tool copies all pages exactly as they appear in the original PDF. Text, images, vector graphics, fonts, and layout are all preserved. The only changes are the removal of unused objects and the regeneration of the document structure. The visual content of the PDF is identical to the original.
What does the reduction percentage and progress bar mean?
The reduction percentage shows how much smaller the compressed PDF is: ((originalSize − compressedSize) / originalSize) × 100. The progress bar visually represents the compressed size as a proportion of the original. A value of 0 or "No change" means the PDF was already clean. A negative value (output larger) is rare but possible for very small PDFs.
Can I compress a password-protected PDF?
The tool uses the ignoreEncryption option in pdf-lib, which allows loading some restricted PDFs (editing restrictions but no open password). PDFs that require a password to open cannot be processed. If the PDF opens without a password but has editing restrictions, the tool may be able to process it.
Is the PDF uploaded to any server during compression?
No. The entire compression process runs in your browser using the pdf-lib JavaScript library. The PDF file data never leaves your device. This makes the tool safe for confidential documents, legal files, financial records, and any other sensitive PDFs.