A PDF that is too large to email, too slow to upload, or over the portal size limit is a common frustration. Compressing it does not require Adobe Acrobat or any desktop software — you can do it directly in your browser, in a few seconds, for free.
This guide shows you how to use the free Online PDF Compressor to reduce your PDF file size, explains the three quality presets and advanced options, and covers what to expect from compression on different types of PDFs.
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100% private — your file never leaves your device
The tool processes your PDF entirely in your browser using pdf-lib. Nothing is uploaded to any server, so sensitive documents stay completely private.
How to compress a PDF online
Upload your PDF
Open the PDF Compressor and drag your file onto the upload area, or click to choose a file. PDFs up to 25 MB are supported. Your file is processed entirely in your browser — it is never sent to any server.
Choose a quality preset
Select Low, Medium, or High quality. Medium is selected by default and works well for most documents. If you need the smallest possible file and can accept some quality loss, choose Low. If quality matters more than size, choose High.
Adjust advanced options (optional)
Three additional options let you fine-tune compression: Optimize Images (on by default), Compress Text (on by default), and Remove Metadata (off by default). For Custom quality, a slider lets you set the exact image quality percentage.
Click Compress PDF
The tool processes your file using pdf-lib in your browser. Compression time depends on file size and how many images are in the document — most files complete in a few seconds.
Review the result and download
After compression the tool shows the original size, compressed size, and the percentage reduction. Click Download to save the file — it is named compressed_[original filename].pdf automatically.
Ready to shrink your PDF?
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Compress PDF free →Understanding the quality presets
The three presets control how aggressively images inside the PDF are resampled. Text-only PDFs see smaller differences between presets; image-heavy PDFs see much larger reductions on Low.
| Preset | Image quality | Best for |
|---|---|---|
| Low | 60% — maximum compression | Web uploads, email attachments where visual quality is less critical |
| Medium (default) | 80% — balanced | Most use cases — good size reduction with acceptable quality |
| High | 95% — minimal compression | Documents where image clarity must be preserved (e.g. medical, legal) |
| Custom | Your choice (slider) | Fine-grained control when presets do not give the result you need |
Advanced compression options
Three toggles give you more control over what gets compressed:
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Optimize Images
On by default
Resamples embedded images at the selected quality level. This typically produces the largest file size reduction. Disable it if your PDF contains no images and you only want text/structure compression.
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Compress Text
On by default
Applies object stream compression to text content and PDF structure. The size reduction is smaller than image optimization but adds up on text-heavy documents.
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Remove Metadata
Off by default
Strips embedded metadata such as author name, creation date, software name, and keywords. Useful for privacy or when sharing externally. The size reduction is small but it cleans up the file.
When do you need to compress a PDF?
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Email attachment limit
Most email providers cap attachments at 10–25 MB. Compressing a PDF often brings it well under the limit without needing to split the file.
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Upload portal restrictions
Job application portals, government forms, and client systems often impose file size limits. Compression gets your document accepted without re-scanning.
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Cloud storage quota
Compressed PDFs take up less space in Google Drive, Dropbox, or OneDrive — useful when managing large collections of documents.
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Website embedding
PDFs embedded in websites load faster when smaller. Compressing a brochure or whitepaper improves page load time for visitors.
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Mobile sharing
Sending PDFs via WhatsApp, Telegram, or iMessage? Compressed files transfer faster and consume less mobile data on both ends.
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Privacy before sharing
Enable "Remove Metadata" to strip author name, creation date, and software information before sending a document externally.
Features & limitations
Fully private — your PDF is processed in your browser using pdf-lib. It is never uploaded to any server.
Four quality levels — Low, Medium, High, and Custom give you control over the trade-off between file size and visual quality.
Shows compression results — the tool displays original size, compressed size, and percentage saved before you download.
25 MB file size limit — the tool cannot process PDFs larger than 25 MB. Try splitting the PDF first, compressing each part, then merging.
Already-compressed PDFs may not shrink further — if a PDF was previously compressed or its images are already at low quality, the reduction will be minimal or zero.
Password-protected PDFs cannot be compressed. Remove the password in your PDF viewer first, then upload the unprotected file.
Frequently asked questions
Is my PDF uploaded to a server when I compress it?
No. The entire compression process runs in your browser using pdf-lib — a JavaScript library that manipulates PDFs locally. Your file is never sent to any server, which means it stays completely private.
How much smaller will my PDF get?
It depends on the content. Image-heavy PDFs (scanned documents, presentations, brochures) typically see 30–70% reduction on Low quality. Text-only PDFs compress much less — often 5–15% — because there are no images to resample. Already-compressed PDFs may see little or no reduction.
Will compression reduce the text quality or make it blurry?
Text is compressed structurally, not re-rendered as an image, so text sharpness is not affected by the quality preset. Only embedded images are resampled. If your PDF contains text rendered as images (common with scanned documents), those will be affected by the quality setting.
What is the difference between "Optimize Images" and the quality preset?
The quality preset sets the target image quality level (60%, 80%, or 95%). "Optimize Images" enables the actual resampling process that uses that quality level. Both need to be active for image compression to occur. Disabling "Optimize Images" skips image resampling regardless of the preset.
My PDF is larger than 25 MB. What can I do?
Try splitting the PDF into two smaller parts first using the PDF Splitter, then compress each part separately. If the original file is a scan, re-scanning at a lower DPI (150 instead of 300) before creating the PDF will produce a much smaller starting file.
Can I compress a password-protected PDF?
No — encrypted PDFs cannot be read by the tool. Remove the password first. In most PDF viewers you can go to File → Print → Save as PDF to create an unprotected copy, then upload that file.
Related PDF tools
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PDF Splitter
Break a large PDF into smaller parts before compressing each separately.
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PDF Merger
Combine multiple compressed PDFs back into a single file.
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PDF Page Numbers
Add page numbers to your compressed PDF before sharing.
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