Microsoft has announced an update for Office for iOS which takes it to version 2.47 (21022805).

With version 2.47, iOS users will now be able to view and edit the Word and PowerPoint files, stored in the cloud, offline on their iPhone and/or iPad device. (Excel workbooks are not supported)

How to download and edit Word/PowerPoint files offline

  1. In the Home screen, tap the More Options menu (triple dot) for the Word document or PowerPoint presentation that you would like to be able to view or edit offline. 
  2. Tap to enable the Make Available Offline toggle.
Files offline IOS

Once the file shows the Downloaded status with a checkmark icon, the file can be viewed and edited offline. 

can now make Word and PowerPoint cloud files available offline in the Office Mobile app as well as the standalone Word and PowerPoint apps for iOS. 

Source: Microsoft