How to Reduce PDF File Size and Manage Image Quality

Why PDFs get so large

File size depends almost entirely on what is embedded inside the PDF:

• ·High-resolution images — larger pixel dimensions and lighter source compression generally increase file size
• ·Scanned pages — each scanned page is stored as a full-resolution image, not compressed text
• ·Embedded fonts — entire font files are included so the document looks correct on any device
• ·Colour profiles and metadata — ICC colour data, document history, and XMP metadata all add bytes

Image-heavy and scanned PDFs often offer more opportunity for size reduction than documents with mostly text and vector content.

The three compression levels explained

• ·Low — renders pages at 300 DPI and encodes them as JPEG at 0.92 quality for the closest result among the available levels.
• ·Medium — renders pages at 200 DPI and uses 0.82 JPEG quality for a balance between output size and visual detail.
• ·High — renders pages at 150 DPI and uses 0.70 JPEG quality for smaller screen-oriented output.
• ·Maximum — renders pages at 96 DPI and uses 0.50 JPEG quality for the smallest available output, with more visible image degradation.

Step-by-step: compress a PDF

1. 1Open editpdfai.com/pdf-compressor and upload your PDF (drag and drop or click to browse).
2. 2Select a compression level. Start with Balanced unless you have a specific reason for Light or Maximum.
3. 3Click Compress PDF.
4. 4Download the compressed file. Compare the reported before and after sizes and inspect text and images at normal zoom.

Realistic expectations by document type

• ·Scanned documents and photo-heavy pages often shrink more because the tool can reduce rendered resolution and JPEG quality.
• ·Text-heavy pages may show smaller gains and lose searchability because the output is flattened to page images.
• ·PDFs that were already aggressively compressed may not become smaller; compare the reported output size before keeping the result.

When not to use maximum compression

• ·Archival copies — use Light to preserve quality for long-term storage
• ·Medical imaging documents — pixel accuracy may be required
• ·Legal exhibits where image clarity can be questioned
• ·Documents that will be printed larger than A4 (compression artefacts become visible)

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