大きすぎるPDFはメールで拒否されがちです。読みやすさを維持しながら縮小する方法を解説します。
問題の概要
スキャン文書や画像の多いレポートはすぐに25MBを超えます。
なぜ起こるのか
PDFはフォント、画像、ベクターを高解像度で埋め込みます。特にスキャンは各ページが大きな画像として保存されます。
ステップバイステップの解決策
- 1Identify whether your PDF is text-based or scanned — the strategy differs.
- 2Open a compression tool and upload the file.
- 3Choose a compression level: high quality for print, medium for email, low for web previews.
- 4Wait for processing, then compare the output size and visual quality.
- 5Download the compressed file and replace the original if the result looks right.
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追加のヒント
- For scans, converting to grayscale can cut size by 30–50%.
- Remove embedded fonts you do not need for the final audience.
- Split very large PDFs first, then compress each part.
- Avoid re-compressing the same PDF many times — quality degrades each pass.
よくある質問
Q.How small can a PDF get?
Text-heavy PDFs can drop by 60–80%; scans depend on original resolution.
Q.Does compression affect text search?
No, as long as the PDF has real text. Image-only scans require OCR to stay searchable.
Q.Will images look pixelated?
Only if you pick aggressive compression. Medium usually looks identical on screen.
Q.Is it safe to compress signed PDFs?
Compression can invalidate digital signatures. Re-sign after compressing if needed.
まとめ
うまく圧縮されたPDFは高速に読み込め、見た目も専門的です。
