Compress PDF Online — Reduce PDF File Size for Free
Shrink your PDF file size online — free, fast, and with full control over quality and DPI. No sign-up needed.
- ✓ Free
- ✓ Quality slider
- ✓ DPI control
- ✓ No watermarks
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Why use PDF99?
Quality slider
Control exactly how aggressively images are re-encoded. High quality (85%+) gives minimal visible change. Lower values produce smaller files at the cost of some image sharpness.
DPI control
Set the target resolution for embedded images. 150 DPI is ideal for most digital uses. 72 DPI is optimal for web or email. 300 DPI retains near-print quality.
Real compression
When PDF.js is available, the tool re-renders each page at your chosen DPI and quality. This produces genuine file size reduction, not just metadata stripping.
No quality loss at high settings
Set quality to 85% or above and the output will be visually indistinguishable from the original.
Fast, local processing
Compression runs in your browser. Your PDF doesn't travel to a remote server.
No size limits
Compress any PDF regardless of how large it is.
What does PDF compression actually do?
PDF compression works by re-encoding the images embedded in the document at lower quality settings and reducing the DPI (dots per inch) at which they're rendered. Images are almost always the largest contributor to PDF file size — a single high-resolution photo can be 3-8MB on its own. By re-rendering pages at 150 DPI and encoding them as JPEG at 75% quality, most image-heavy PDFs shrink by 40-70% with no visible change at normal reading sizes.
Text content in PDFs is already stored efficiently and contributes little to overall size. Compressing a text-only document produces modest size reduction — mainly from stripping metadata and revision history. The dramatic reductions (50-80%) happen with scanned documents and image-heavy files.
What is a PDF file?
A PDF (Portable Document Format) is one of the most popular document formats used for sharing and storing digital files. It preserves the original layout, fonts, images, and formatting regardless of the device or operating system being used. PDFs are commonly used for resumes, invoices, contracts, eBooks, manuals, reports, and scanned documents because they appear the same for every viewer.
PDF files are widely supported across computers, smartphones, tablets, and web browsers, making them the preferred format for professional and personal document sharing. They can also include hyperlinks, forms, digital signatures, and password protection, making PDFs both versatile and secure for everyday use.
How to compress a PDF
Upload your PDF
Choose your PDF using the file picker or drag it onto the upload area.
Set quality and DPI
Adjust the quality slider and DPI to balance file size against image quality.
Download the result
Click Compress PDF and download your smaller file instantly.
Frequently asked questions
It depends on the content. Image-heavy PDFs compress well — often 30–70%. Text-only PDFs may shrink 10–20%. A PDF already optimised may barely change.
Quality controls how aggressively images are re-encoded (lower = smaller but blurrier). DPI controls the resolution of re-rendered pages (lower = smaller, less sharp).
No. Compress any PDF regardless of size.
Yes. Compression runs in your browser. Your PDF is not sent to a remote server.
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