Compress PDF Online

PDF has become the universal format for sharing documents — reports, contracts, brochures, invoices and presentations all circulate as PDF files every day. Yet many PDFs are far larger than they need to be. A single-page brochure containing embedded high-resolution images can easily exceed 20 MB, making it too large to email, too slow to load in a browser and too heavy for document management systems with upload limits. PDF compression addresses this directly, reducing file size while keeping text perfectly sharp, hyperlinks active and the overall layout intact.

Why PDF Files Become Oversized

The most common cause of bloated PDFs is embedded images that have not been optimised for screen or print distribution. Design tools such as Adobe InDesign and Microsoft Word embed images at the full resolution they were originally created in — sometimes 300 DPI or higher — regardless of whether that resolution is needed in the final document. A ten-page report with a dozen high-resolution photographs can balloon to 50 MB even though it could look identical to readers at one-tenth that size.

Other contributors include redundant font data, unused object streams, embedded preview thumbnails and duplicated resources. Our Ghostscript-powered compressor identifies and removes all of these, applying multi-level image downsampling and lossless optimisation to produce the smallest possible file without compromising readability.

How Our PDF Compressor Works

Under the hood, our PDF compressor uses Ghostscript — the industry-standard PostScript and PDF interpreter used in professional print workflows for decades. The compression pipeline is fully automated:

1. Your PDF is uploaded securely and passed to the Ghostscript engine for analysis.
2. Embedded images are identified and re-sampled to the target resolution — typically 150 DPI for screen-optimised output or 300 DPI for print-quality output.
3. Redundant resources such as unused fonts, duplicate streams and embedded thumbnails are stripped from the file structure.
4. The document is reconstructed as a clean, linearised PDF optimised for fast web viewing.
5. A private, signed download link is created and the source file is permanently deleted after two hours.

Compression Level Guide

Tips for Compressing PDFs Effectively

• Use the "Screen" compression level for email attachments and online forms — readers on screens cannot distinguish 72 DPI images from 300 DPI at standard viewing distances.
• For PDFs that will be printed at home or in an office, "Printer" quality preserves enough detail for crisp output on standard inkjet and laser printers.
• Scanned PDFs typically benefit the most from compression, since their content is entirely image-based and highly compressible.
• Text-only PDFs are already small; expect modest reductions from compressing them compared to image-heavy documents.
• Always test the compressed PDF on screen before sending — zoom in on any text-heavy pages to confirm readability has been preserved.

When emailing a PDF, the "Screen" preset almost always produces the best result. Most email clients display PDFs on screen, not in print, so 72 DPI imagery looks perfectly sharp to the recipient while keeping the attachment well under any size limit.

MultiCompressor's PDF compressor removes the complexity of working with Ghostscript directly, giving you professional-grade PDF optimisation through a clean, simple interface. Upload your document, select a compression level that suits your use case and download a leaner PDF that is ready to share — no software installation, no account and no file stored beyond the two-hour processing window.