Can iCloud drive be used for sharing documents produced by third-party apps? I have upgraded to Yosemite and iOS8.02 on all my devices, including a MacBook Pro, an iPad2, an iPad Mini, and an iPhone 5c.

I understand that one can use iCloud Drive to share documents produced by any of the iWork apps and also some third-party apps that have been specifically upgraded to use iCloud drive (such as the Readdle suite of apps and Day One).

But, what about the other third-party apps that have not been specifically upgraded? Can files from these apps also be shared on iCloud Drive? 

I don't use Pages, Numbers, and Keynote all that much.  In fact, I prefer Microsoft Office for Mac.  And I have a lot of third-party apps I use a lot more often than any of the former.  And, it does not seem to me that all that many of the third-party apps have been specifically prepared to accommodate iCloud drive.

Unless I am missing something, it would seem to me that it is not necessary for me to upgrade to iCloud drive.  Do you have any advice or comments about this?  Is there anywhere where I might find a list of third-party apps now set up for iCloud Drive?
To take advantages of iCloud Drive, the third-party apps need to implement the Document Provider Extension so you can share those files and send them to iCloud Drive. I’ve explained it in one of the post I’ve written:

Not to confuse document provider extension with share extension where you can only send and upload selected files, document provider extension provides more options to export, import, open, and move files between document storage providers.
The basic functionality each document provider extension supports is export and import. It lets the extension to export or import the files to destination path. To see this extension in action, you may update to the latest Dropbox and turn it on from the More button in Files.

Basically, you can share files from Microsoft Office to iCloud Drive as long they support Share Extension Point or the Export, Import in Document Provider Extension Point.