Yes, you can.
All you need to do is save the file to Mobile Documents, which is located in your (hidden) user library. Anything put into Mobile Documents is automatically uploaded to iCloud.
It's kind of difficult to find the Mobile Documents folder, however, so I recommend doing the following:
1. In Finder, open the Go menu. Hold the Option key down and you'll see your Library (which is actually in Users/[your user name]/Library, but is normally hidden). Select it.
2. In your LIbrary you'll see Mobile Documents. Make an ALIAS of this (**DO NOT** move the actual folder, make an alias ONLY) by selecting it and then pressing command-L.
3. Place this alias anywhere you want. I suggest your home folder's Documents folder, but you could even put it on the desktop if you really want to.
Then just save Pages files to that alias, and they will also be available in iCloud.