How to compress a PDF

Reduce PDF file size for email attachments, uploads with size limits, or storage.

Short answer: use the Compress PDF tool. It re-renders pages at a lower image quality and scale, producing a smaller file.

Why PDFs get large

• High-resolution scans. A scan at 600 dpi can be 10× the size of the same content at 150 dpi.
• Embedded fonts. Every font used must be embedded, adding hundreds of KB per family.
• Uncompressed images. Some PDFs store images as raw bitmaps instead of JPEG.
• Layers and metadata. Editing history, annotations and application-specific data accumulate.

How compression works

Omni PDF's compressor renders each page to a JPEG at a chosen quality and resolution, then rebuilds a new PDF from those images. The result is usually much smaller — sometimes 5–10× — but text becomes part of the raster and is no longer selectable or searchable.

Quality vs size

• Quality 0.5, scale 1.0 — maximum compression. Good for email previews.
• Quality 0.7, scale 1.4 — balanced. Standard for most documents.
• Quality 0.9, scale 2.0 — light compression. Preserves detail; small size reduction.

When not to compress

Don't compress PDFs that:

• Contain searchable text you need to keep
• Are already small (under 500 KB)
• Contain vector illustrations where crisp edges matter
• Have legal or archival requirements

Always compare the compressed file to the original before deleting the source.