Short answer
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 does this on your iPhone: it scans to a clean PDF, runs on-device OCR, and can lock files with Face ID — a pay-once app with no subscription. Check the App Store listing for current features.
What to look for before choosing
- 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
A practical decision process
- 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.
Quick comparison
| Need | What to check | Why it matters |
|---|---|---|
| Pricing model | Check whether useful features require a subscription, a one-time unlock, or neither. | The cheapest app on day one may not be cheapest after a year. |
| Privacy model | Prefer on-device work when the content is sensitive. | Private documents, resumes, study data, and family content deserve careful handling. |
| Export / lock-in | Confirm file formats, sharing, backup, and deletion controls. | A good app should help you finish the task, not trap your work. |
Where ScanTo Pro fits
ScanTo Pro is a strong fit when you want private, on-device scanning without a subscription.
Pay onceNo subscriptionOn-device
This page is an independent buying guide. App Store features and prices can change, so confirm details on the listing before purchase.