Compressing a PDF sounds simple — but the result depends heavily on DPI settings, image content, and compression level. This guide explains exactly what happens inside a PDF when you compress it.
PDF compression reduces file size by doing one or more of the following:
Text and vector graphics survive compression with zero quality loss. Images are where quality trade-offs happen.
DPI (Dots Per Inch) is the resolution of images embedded in a PDF. Higher DPI = sharper images = larger file size.
| DPI | Use case | Quality | Typical image size |
|---|---|---|---|
| 72 DPI | Screen viewing only | Low — blurry when printed | ~50–150 KB/image |
| 96 DPI | Web, email attachments | Acceptable on screen | ~80–200 KB/image |
| 150 DPI | Office printing | Good for most documents | ~200–500 KB/image |
| 300 DPI | Professional printing | High — sharp and clear | ~500 KB–2 MB/image |
| 600 DPI | Photography, archival | Very high | ~2–8 MB/image |
Reduces file size 20–40%. No visible quality loss. Images stay at 150–200 DPI. Safe for printing and sharing.
Reduces file size 40–70%. Images downsampled to 96–150 DPI. Text stays sharp. Photos may show slight softness on close inspection.
Reduces file size 60–90%. Images downsampled to 72 DPI. Text remains readable on screen but printing quality suffers. Use only when file size is critical.
Results vary significantly based on content type:
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Open PDF Compressor →It depends on the level. Light compression has no visible quality loss. Heavy compression reduces image resolution and may make photos look blurry, though text usually stays sharp.
300 DPI is the standard for professional print quality. 150 DPI is acceptable for everyday office printing. 72–96 DPI is screen-only and will look blurry when printed.
Large PDFs usually contain high-resolution images, embedded fonts, or scanned pages stored as full-resolution images. Compressing reduces image resolution and strips unused data.
Image-heavy and scanned PDFs can be reduced 60–90%. Text-only PDFs compress 10–30% since text is already compact data.