PDF Compressor Online — Reduce PDF Size Up to 90% Free

A PDF compressor online reduces the file size of PDF documents by re-encoding images, deduplicating objects, and stripping unnecessary data. Keynou's compressor runs entirely in your browser — your files never get uploaded to a server. Choose from multiple compression levels and reduce PDF size by up to 90% while preserving readable quality.

How PDF Compression Works

PDF files can be large for several reasons: high-resolution embedded images, duplicate font data, uncompressed streams, and metadata that isn't needed for display. Compression targets each of these:

Image Compression

Most of the file size in a typical PDF comes from embedded images. The compressor re-encodes images at optimized resolutions and quality levels:

• Resampling — reduces image resolution to match typical display needs (150 DPI for screen, 300 DPI for print)
• Recompression — converts uncompressed or losslessly compressed images to JPEG, which is far smaller for photographic content
• Color optimization — reduces color depth where possible (e.g., converting 32-bit to 24-bit)

Text and Stream Optimization

• Stream compression — applies FlateDecode (zlib) compression to uncompressed content streams
• Font subsetting — embeds only the characters actually used in the document instead of entire font files
• Object deduplication — removes duplicate objects and consolidates shared resources

Metadata Cleanup

• Strips unnecessary metadata (author info, creation tool, edit history)
• Removes unused embedded fonts and color profiles
• Eliminates redundant cross-reference data

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  <text x="375" y="35" fill="#1e293b" font-size="16" font-family="sans-serif" text-anchor="middle" font-weight="bold">PDF Compression: Before & After</text>
  <!-- Before bar -->
  <text x="100" y="75" fill="#1e293b" font-size="13" font-family="sans-serif" text-anchor="middle" font-weight="bold">Before</text>
  <rect x="30" y="85" width="300" height="50" fill="#ef4444" rx="6"/>
  <text x="180" y="116" fill="white" font-size="16" font-family="sans-serif" text-anchor="middle" font-weight="bold">12.4 MB</text>
  <text x="100" y="155" fill="#64748b" font-size="11" font-family="sans-serif" text-anchor="middle">Original PDF with high-res images</text>
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  <text x="370" y="100" fill="#8b5cf6" font-size="11" font-family="sans-serif" text-anchor="middle" font-weight="bold">Compress</text>
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  <text x="560" y="75" fill="#1e293b" font-size="13" font-family="sans-serif" text-anchor="middle" font-weight="bold">After</text>
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  <text x="465" y="116" fill="white" font-size="16" font-family="sans-serif" text-anchor="middle" font-weight="bold">1.2 MB</text>
  <text x="560" y="155" fill="#64748b" font-size="11" font-family="sans-serif" text-anchor="middle">90% smaller — same readable content</text>
  <!-- Compression levels -->
  <text x="375" y="195" fill="#1e293b" font-size="13" font-family="sans-serif" text-anchor="middle" font-weight="bold">Compression Levels</text>
  <rect x="80" y="210" width="160" height="40" fill="#fbbf24" rx="5"/>
  <text x="160" y="235" fill="#78350f" font-size="12" font-family="sans-serif" text-anchor="middle" font-weight="bold">Light (~50%)</text>
  <rect x="260" y="210" width="160" height="40" fill="#60a5fa" rx="5"/>
  <text x="340" y="235" fill="#1e3a5f" font-size="12" font-family="sans-serif" text-anchor="middle" font-weight="bold">Medium (~70%)</text>
  <rect x="440" y="210" width="160" height="40" fill="#34d399" rx="5"/>
  <text x="520" y="235" fill="#064e3b" font-size="12" font-family="sans-serif" text-anchor="middle" font-weight="bold">Strong (~90%)</text>
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  </defs>
</svg>

Compression Levels

Keynou's PDF compressor offers three compression levels to balance file size against quality:

Light Compression (~50% reduction)

• Image quality: High — minimal visible difference
• Best for: Documents where image quality is important (portfolios, design proofs)
• What it does: Optimizes streams, subsets fonts, strips metadata, lightly resamples images

Medium Compression (~70% reduction)

• Image quality: Good — slight softening of high-res images, text remains crisp
• Best for: General use — email attachments, web downloads, document sharing
• What it does: Resamples images to 150 DPI, recompresses as JPEG, removes duplicate objects

Strong Compression (~90% reduction)

• Image quality: Reduced — noticeable in image-heavy documents, text remains readable
• Best for: Email attachments with strict size limits, web uploads, archival storage
• What it does: Resamples images to 72–100 DPI, aggressive JPEG compression, removes all non-essential data

Image vs. Text Compression

Understanding what contributes to your PDF's file size helps you choose the right compression level.

Image-Heavy PDFs

PDFs containing photographs, scanned documents, or graphics are primarily image data. A 20-page scanned document can easily be 15MB because each page is a full-resolution image. Strong compression can reduce this to 1–2MB by resampling images to screen resolution.

Text-Heavy PDFs

PDFs that are mostly text with few or no images are already quite small. A 50-page text-only PDF might be 200KB. Compression of these files yields modest reductions (10–30%) since there's little image data to optimize. The main savings come from font subsetting and stream compression.

Mixed PDFs

Most real-world documents — reports, presentations, brochures — contain a mix of text and images. Compression targets the image content for the biggest savings while keeping text crisp and readable regardless of compression level.

Step-by-Step: Compress a PDF Online

Step 1: Open the Compressor

Go to the PDF compressor. No login required.

Step 2: Load Your PDF

Drag and drop your file or click to browse. The file loads into browser memory — no upload occurs.

Step 3: Choose Compression Level

Select Light, Medium, or Strong based on your needs (see the comparison above).

Step 4: Compress and Download

Click "Compress PDF." The browser processes your file and generates the compressed version. Download it immediately.

Step 5: Verify Quality

Open the compressed PDF and check that:

• Text is crisp and readable
• Images are acceptable quality for your use case
• All pages are present
• Interactive elements (links, bookmarks) still work

Browser-Based Privacy

The entire compression process runs in your browser. Your PDF is read from disk into memory, compressed using client-side JavaScript, and output as a download — no file is transmitted to any server.

This matters for documents containing:

• Financial statements and tax records
• Legal contracts and court filings
• Medical records and insurance documents
• Personal identification documents
• Confidential business reports

No upload, no server storage, no data retention, no account required. You can read more about client-side file handling in the MDN File API documentation.

Common Use Cases

Email Attachments

Most email providers limit attachments to 10–25MB. A 15MB PDF won't send through Gmail's 25MB limit if you're attaching other files. Compress it to 2MB and the email sends without issues.

Web Uploads

Many online forms, government portals, and application systems impose strict file size limits (often 2–5MB). Compress your PDF to meet these requirements without splitting the document.

Website Downloads

If you offer PDF downloads on your website, large files slow down page load and consume bandwidth. Compressed PDFs download faster and improve user experience. According to Google's PageSpeed guidelines, faster downloads reduce bounce rates.

Cloud Storage

Compress PDFs before uploading to Google Drive, Dropbox, or OneDrive to save storage space — especially useful when approaching free tier limits.

Mobile Sharing

Smaller PDFs transfer faster over mobile networks and use less data. This matters when sharing documents via WhatsApp, email, or cloud links on cellular connections.

Keynou vs. iLovePDF for PDF Compression

iLovePDF is a popular PDF compressor, but the processing model differs:

Feature	Keynou	iLovePDF
Processing	Browser-based	Cloud server
File upload	No	Yes
Free file size limit	No server limit	200MB
Compression levels	3 (Light/Medium/Strong)	3 (Basic/Strong)
Account required	No	Required for some features
Privacy	File never leaves device	Uploaded to their servers
Watermark	None	None

iLovePDF works well, but every file you compress passes through their server infrastructure. For sensitive documents, Keynou's browser-based approach is the safer choice.

Tips for Best Compression Results

1. Match the level to your use case — Don't use Strong compression for a design portfolio where image quality matters. Use Light or Medium instead.

2. Check text quality after compression — Text should remain crisp at all compression levels. If text looks blurry, the PDF may contain text rendered as images (scanned document) rather than actual text.

3. Compress before merging — If you're combining multiple PDFs, compress each one first. This reduces memory usage during merging and produces a smaller final file.

4. Try different levels — If Strong compression degrades quality too much, try Medium. The difference between 70% and 90% reduction is often a quality tradeoff you can evaluate visually.

5. Compress images before creating the PDF — If you control the source, reduce image resolution before creating the PDF. This produces better results than compressing after the fact.

Frequently Asked Questions

Will compression affect text quality?

No. Text in PDFs is stored as vector data, not pixels. Compression targets images and metadata — text remains crisp at all compression levels.

Can I compress a password-protected PDF?

No. Remove the password first using your PDF viewer, then compress the unlocked file.

How much can I expect to reduce file size?

It depends on the content. Image-heavy PDFs can shrink by 80–90%. Text-heavy PDFs typically shrink by 10–30%. Most mixed-content documents compress by 50–70%.

Does compression remove links and bookmarks?

Light and Medium compression preserve links and bookmarks. Strong compression may remove some interactive elements to maximize size reduction.

Is there a file size limit?

Since processing is browser-based, the limit is your device's available memory. Most modern browsers handle PDFs well beyond cloud-based free tier limits.

Related Tools

• PDF Compressor — Compress PDF files to reduce size
• Compress PDF — Alternative compression tool
• Image Compressor — Compress images before embedding in PDFs
• PDF Merger — Combine PDFs after compressing each file

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Published: August 20, 2026
Category: PDF Tools
Reading Time: 7 minutes