Currently you would need to purchase a third party app to do this. There is an OS update, 4.5, in the works that has some of this functionality built in called DocsToGo which should be out by September.
With the 4.5 update you will only be able to make limited changes to existing documents. No new document creation at all. However you will be able to purchase an upgrade for about $70.00 to get full functionality.
Posted from my CrackBerry at wapforums.crackberry.com