iOS and iPadOS are designed with a sandboxed storage architecture, which means users do not have direct access to the device’s internal storage or to the underlying system folders and application folders.
Unlike a Mac or Windows PC, you cannot open the iPhone or iPad’s internal storage and browse through its complete directory structure. You can access files and folders that are intentionally exposed through the Files app, such as files stored in On My iPhone/iPad, iCloud Drive, or other supported cloud-storage providers.
Similarly, each third-party app has its own private sandbox. The data belonging to one app is normally accessible only to that app. Other apps, and even the Files app, cannot simply browse into that app’s private data folder unless the app developer specifically provides an appropriate sharing or export mechanism.
This is an important security and privacy feature. It prevents one app from freely accessing another app’s private data, which helps protect personal information such as databases, credentials, settings, cached content, and other application-specific files.
Therefore, app-specific data cannot generally be copied or transferred directly to a USB flash drive (pendrive) using the Files app. A USB drive can be connected to an iPhone or iPad, and you can copy supported files to and from it, but only files that iOS/iPadOS makes available through the Files app or through an app's own Share, Export, Backup, or Save function can be transferred.
For example, if an app stores its documents in a location that it exposes through the Files app, you can copy those documents to a USB drive. However, you cannot use the Files app to navigate into the app's private sandbox and copy its entire internal data folder.
There are therefore two very different things to distinguish:
- Files and folders exposed through the Files app — these can generally be copied, moved, renamed, or transferred to external storage, subject to the app's permissions.
- Private application data stored inside an app's sandbox — this is controlled by iOS/iPadOS and is not directly accessible to the user or to another app.
If the objective is to move an app's data to another iPhone or iPad, the appropriate method is normally to use the app's own transfer/export facility, iCloud synchronization, an encrypted device backup and restore, or another transfer mechanism provided by the app developer. Simply copying the app's internal folder to a pendrive and putting it on another device is not supported by iOS/iPadOS.
This restriction is intentional—it is not a limitation of the USB drive. The USB drive can store the data, but iOS/iPadOS decides which data you are permitted to access and copy in the first place.
