iOS apps written to take advantage of iCloud Drive can additionally export their files to an iCloud Drive folder. We'll use Pages again.
Within Pages open a document, tap the Share icon, and tap Send a Copy. In the Send a Copy window that appears choose an output format (Pages, PDF, Word, or ePub). The file will be converted and a Choose How to Send window will appear. Tap on Send To and the iCloud window appears. Tap a folder where you'd like to store the document and, at the bottom of the resulting window, tap Export to this location. The file will be copied to that folder on your iCloud Drive.
Better but still limited
iCloud Drive is less flexible than other cloud storage services, such as Dropbox, Box.com, Google Drive, OneDrive, and MediaFire. Outside of the options available in the Sharing menu you can't share and sync your iCloud Drive documents with others, for example, thus making document collaboration tricky. With these third-party storage services you can send a link to anyone so they can download a file. With iCloud Drive you can share files this way only with documents created with iWork apps. iCloud Drive has other limitations as well. You'll need OS X Yosemite and iOS 8 and you can't save files larger than 15GB, for example.
Also, large amounts of additional storage is more expensive than from competing services. While you get 5GB of storage for free (which you share across all your iCloud-associated devices), 1TB of storage costs $20 a month. Dropbox offers 1TB for only $10 a month. However, you can purchase additional iCloud storage in smaller increments than Dropbox allows. For example, you can get 20GB of additional storage for $.99 a month and 200GB for $3.99 a year.
For now, iCloud Drive is a useful way to access some of your files on different devices including Macs, Windows PCs, and iOS devices. As time goes on it will become more helpful as additional third-party apps are updated to take advantage of it.
Sign up for CIO Asia eNewsletters.