By default, Nutrient tries to save annotations into PDFs. If this fails (e.g. if the file is in a nonwritable location), it’ll use the fallback store. This store is located at `/Library/PrivateDocuments/PSPDFKit`.

Each document is referenced by its unique `UID`. Annotations are saved as binary objects.

Next, there’s the image cache at `/Library/Caches/PSPDFKit`. You can control if and how much is saved by customizing the global [`PDFCache`](https://www.nutrient.io/api/ios/documentation/pspdfkit/pdfcache) object. This folder is also cleared when a device is running low on memory.

Lastly, some external data is saved in `/tmp/PSPDFKit`. This data mostly consists of video files that need to be unpacked before they can be displayed. This filter will be cleaned up by the OS on every cold boot of the device or in low memory situations.
---

## Related pages

- [Advanced CocoaPods integration](/guides/ios/miscellaneous/advanced-cocoapods-integration.md)
- [App Transport Security](/guides/ios/pspdfkit-instant/app-transport-security.md)
- [Advanced Carthage integration](/guides/ios/miscellaneous/advanced-carthage-integration.md)
- [Bitcode](/guides/ios/faq/bitcode.md)
- [Carthage integration](/guides/ios/best-practices/carthage-integration.md)
- [Framework Size](/guides/ios/faq/framework-size.md)
- [Airdrop](/guides/ios/features/airdrop.md)
- [Customizing The Page Number](/guides/ios/customizing-pdf-pages/customizing-the-page-number.md)
- [Nightly Builds](/guides/ios/best-practices/nightly-builds.md)
- [About Memory Usage](/guides/ios/memory-and-storage/about-memory-usage.md)
- [Customizing the log level on iOS](/guides/ios/features/logging.md)
- [iOS PDF SDK security](/guides/ios/faq/sdk-security.md)
- [Powered By Nutrient](/guides/ios/miscellaneous/powered-by-nutrient.md)
- [Optimize PDF documents for mobile rendering on iOS](/guides/ios/miscellaneous/optimize-pdf-documents-for-mobile-rendering.md)
- [Third Party Compatibility](/guides/ios/miscellaneous/third-party-compatibility.md)
- [Reduce App Size](/guides/ios/best-practices/reduce-app-size.md)
- [Modifying permissions in your iOS app](/guides/ios/getting-started/permissions.md)
- [Transferring File Edits To A Server](/guides/ios/best-practices/transferring-file-edits-to-a-server.md)
- [Using Document Efficiently](/guides/ios/getting-started/using-document-efficiently.md)
- [Using Automatic Saving Safely](/guides/ios/best-practices/using-automatic-saving-safely.md)
- [Manage your iOS status bar with view controllers](/guides/ios/faq/view-controller-based-status-bar-appearance.md)
- [Strategies For Multiple Bundle Ids](/guides/ios/faq/strategies-for-multiple-bundle-ids.md)
- [Youtube Links](/guides/ios/miscellaneous/youtube-links.md)
- [Version Numbering](/guides/ios/best-practices/version-numbering.md)