how to reduce pdf file size on iphone
iOS does not include a dedicated 'Compress PDF' button in the native Files app as of iOS 18/26; the most common workaround is the Print-to-PDF trick (open PDF → Share → Print → pinch out → Share → Save to Files), which re-renders and re-compresses the embedded images, often producing a smaller file — but results are unpredictable and quality may degrade. The most effective approach is at the point of scanning: setting a lower DPI (150 DPI is generally sufficient for readable text), using JPEG compression rather than lossless, and scanning in grayscale or black-and-white mode instead of colour can reduce file size by 60–80% compared to defaults.
簡短回答
iOS does not include a dedicated 'Compress PDF' button in the native Files app as of iOS 18/26; the most common workaround is the Print-to-PDF trick (open PDF → Share → Print → pinch out → Share → Save to Files), which re-renders and re-compresses the embedded images, often producing a smaller file — but results are unpredictable and quality may degrade. The most effective approach is at the point of scanning: setting a lower DPI (150 DPI is generally sufficient for readable text), using JPEG compression rather than lossless, and scanning in grayscale or black-and-white mode instead of colour can reduce file size by 60–80% compared to defaults. Dedicated scanner and PDF apps expose these controls directly and are the reliable path to predictable compression.
ScanTo Pro 在 iPhone 上就能辦到:掃成乾淨的 PDF、在裝置上跑 OCR,還能用 Face ID 鎖住檔案,而且是買斷制、沒有訂閱。最新功能請見 App Store 商店頁面。
挑選前要注意什麼
- iOS native 'Print to PDF' workaround can reduce file size but results are inconsistent
- Scan resolution (DPI) is the biggest lever: 150 DPI gives readable text; 300 DPI for archival quality
- JPEG compression level directly trades off file size against image quality (blocking artifacts at extreme compression)
- Grayscale or black-and-white mode significantly shrinks colour scan PDFs with no text quality loss
- True PDF compression (resampling, removing metadata, flattening layers) requires a dedicated app
實用的決策步驟
- iOS native 'Print to PDF' workaround can reduce file size but results are inconsistent.
- Scan resolution (DPI) is the biggest lever: 150 DPI gives readable text; 300 DPI for archival quality.
- JPEG compression level directly trades off file size against image quality (blocking artifacts at extreme compression).
- Grayscale or black-and-white mode significantly shrinks colour scan PDFs with no text quality loss.
- True PDF compression (resampling, removing metadata, flattening layers) requires a dedicated app.
快速比較
| 需求 | 要確認什麼 | 為什麼重要 |
|---|---|---|
| 定價模式 | 確認實用功能是需要訂閱、一次性解鎖,還是都不用。 | 第一天最便宜的 App,一年後不一定最便宜。 |
| 隱私模式 | 內容敏感時,優先選在裝置上處理的 App。 | 私人文件、履歷、學習資料與家庭內容,都值得謹慎對待。 |
| 匯出/綁定 | 確認檔案格式、分享、備份與刪除的控制權。 | 好的 App 應該幫你完成任務,而不是把你的成果綁死。 |
ScanTo Pro 適合哪些情境
如果你想要不必訂閱、又完全在裝置上處理的私密掃描,ScanTo Pro 很合適。
一次買斷無訂閱裝置端處理
這是由 App 開發團隊親自撰寫的購買指南。App Store 的功能與價格可能會有變動，請在購買前至商店頁面確認詳細資訊。
常見問題
What DPI should I use for an everyday text document scan?
150 DPI produces clearly readable text in a reasonably small file and is a common default in quality scanner apps. Use 300 DPI for fine print, small fonts, or documents you may need to print later.
Does converting a scan to black-and-white reduce file size?
Yes — significantly. A black-and-white (binary) scan of a text document can be 5–10× smaller than the same page scanned in colour, with no loss of text readability. It is not suitable for preserving photos or colour graphics.
Will compressing a PDF damage its embedded OCR text layer?
Compressing the image layer (reducing DPI or JPEG quality) does not remove an existing OCR text layer embedded in the PDF. However, if you re-scan or re-render the document, the OCR layer may need to be regenerated.