What is PDF Compressor?
PDF Compressor is a free browser-based PDF tool powered by PDF-lib. Your documents are processed entirely in your browser and never sent to any server. Works with any standard PDF file. No Adobe Acrobat or software installation needed.
This tool lets you reduce pdf file size in your browser without installing any software or creating an account. Everything runs directly in your browser for maximum privacy. Your files and data never leave your device.
Use it for quick tasks at any time from any device — desktop, tablet or mobile. No subscription, no ads, no limits.
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Instant results
No server processing or wait
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100% private
Files stay on your device
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Always free
No subscription or fees
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Mobile ready
Works on any device
How to use PDF Compressor
- Upload your PDF file — drag and drop or click to browse
- Select compression level: low, medium or high depending on your needs
- Click Compress and watch the file size reduction percentage appear
- Download your compressed PDF — typically 40–80% smaller for image-heavy files
Why use OnlineToolsPlus?
PDF tools on OnlineToolsPlus use PDF-lib — a JavaScript PDF engine that runs locally in your browser. Your documents are never uploaded to a server, which means no privacy risk for sensitive contracts, financial documents or personal files. With 25+ free PDF tools covering merging, splitting, compressing, editing and converting, you have a complete PDF toolkit at no cost.
Frequently asked questions
How much does PDF compression reduce file size?
Results vary widely depending on the source content. PDFs that consist mostly of scanned images or embedded photographs can be reduced by 70–90% with moderate quality loss, or 40–60% with negligible quality loss. PDFs made from digital text (Word exports, spreadsheets) are already compact and may compress only 10–20% since there are few images to recompress.
Will compressed text still be selectable and searchable?
Yes. Text in digital PDFs is stored as vector data separate from images. Compression targets image data and removes unused objects. The text layer is unaffected — it remains selectable, copyable, and searchable after compression.
Will compression make my PDF look worse?
At moderate compression settings, the difference is usually invisible on screen and in normal print. Very aggressive compression shows as image blurriness or JPEG artifacts, particularly in photos and scanned documents. The tool offers quality settings so you can balance file size against visual quality. Always keep the original file and test the compressed version before distributing.
Can I compress a scanned PDF?
Yes. Scanned PDFs are image-based and benefit the most from compression. The tool recompresses the embedded page images at the quality level you choose. For scanned text documents, quality 70–80% is usually sufficient for comfortable on-screen reading. For scanned documents with fine print or diagrams, use quality 85–90%.
Are my documents uploaded to a server?
No. PDF compression runs entirely in your browser using PDF-lib. No file is ever sent to any server. This is critical for PDFs containing contracts, financial statements, medical records, or other sensitive information — they never leave your device.
Can I compress a password-protected PDF?
Password-protected PDFs must be unlocked before compression. Use the PDF Unlock tool on OnlineToolsPlus first, then compress the unlocked copy.
Is there a file size limit?
No. The tool runs in your browser with no server involved. Very large PDFs (100+ MB) may take 30–60 seconds to process on older devices, but will compress correctly. Close other browser tabs to free up memory when processing large files.
Does compression affect PDF forms or digital signatures?
Compression may invalidate digital signatures, as signatures protect the file's byte content. If your PDF has a verified digital signature that must remain valid, do not compress it. PDF form fields are generally preserved, but it is good practice to test the output before distributing.
What is the difference between PDF compression and PDF optimization?
Compression specifically refers to recompressing embedded images at lower quality to reduce size. Optimization is broader — it includes compression plus removing unused objects, cleaning revision history, subsetting fonts, and merging duplicate resources. The result is a smaller, cleaner file. This tool performs both compression and optimization in one step.
Can I compress multiple PDFs at once?
The current tool processes one PDF at a time. Each compression is fast — typically 2–10 seconds for most documents. For batch compression of many PDFs, Adobe Acrobat Pro's batch processing or command-line tools like Ghostscript are more efficient.
- Email attachment: Under 10 MB is safe for most email servers. Under 5 MB is ideal for mobile recipients.
- Website download: Under 2 MB for documents users will preview in a browser. Under 500 KB for documents embedded in pages.
- Court filing / legal submission: Many court systems cap uploads at 5–25 MB per document. Check requirements before compressing to avoid losing required quality.
- Archival copy: Keep a full-quality version. Compress only the working copy or distribution version.
- WhatsApp / Telegram: WhatsApp has a 100 MB document limit. Telegram allows up to 2 GB. For most use cases, under 20 MB is comfortable.
Target File Sizes for Common Scenarios
- Embedded images: The single biggest contributor to PDF file size. A PDF with a dozen high-resolution photos can easily be 20–50 MB. Recompressing embedded images at lower quality is the most impactful compression step.
- Embedded fonts: PDFs embed font data to ensure correct display on all devices. A single font can add 50–200 KB. Using system fonts or subsetting (embedding only used characters) reduces this significantly.
- Scanned pages: A scanned document stores each page as a full-resolution image. A 300 DPI A4 scan produces a 2480 × 3508 px image. Reducing scan resolution to 150 DPI cuts file size by 75% with no visible difference at screen resolution.
- Unused objects and metadata: PDFs accumulate revision history, deleted objects, and metadata over repeated edits. Cleaning these up with PDF optimization removes hidden bloat.
Understanding what makes PDFs large helps you choose the right compression approach:
Why PDF Files Get So Large
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Last updated: April 11, 2026
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