Mark files or folders "offline" to read them anytime, even when you aren't connected to the Internet. Online edits made to the files sync the next time your iPad, iPhone or iPod Touch connects to the Web, so you get the latest version of the file.
Files or folders marked offline are read-only - you can edit the them only when you're online. If you edit a file offline, it saves as a new file, and does not change the original OneDrive file.
Taking folders offline is available for Premium OneDrive with an Office 365 subscription.
In the OneDrive app, select the file or folder that you want available for offline reading, then tap Keep offline .
Files or folders marked for offline reading have the Keep offline icon in the List view. Tap the file listing anytime to open the file for reading.
Tip: Once you mark a file or folder offline, OneDrive also lists it in an Offline Files view. Tap the Me icon at the bottom of the screen, tap Offline Files to instantly find all your offline files and folders.
To stop keeping a file or folder offline, select the offline file or folder and tap Online only .