If you have Google Drive on you iPad, you can use the Files app to copy/move files between iCloud Drive and Google Drive.
If you don’t see Google Drive in the files app, tap the (…) icon at the top of the files list and choose Edit. Google Drive should show up with a switch next to it that you can enable.
Once you can see Google Drive, navigate to the iCloud Drive you want to move, select it, then choose to Move it. In the dialog navigate to the Google Drive option, and to the folder you want (if that appears). Choose copy to finish. Because you are moving between different types of storage, the file won’t actualy move. It will be copied. If you want the original deleted you’ll have to do that as a separate action.
Once it is in Google Drive, you should be able to access the file in Google Docs.
Depending on the app and the file type, you may also see Google Docs and/or Google Drive in the share sheet. That should also work.
I rarely use Google Drive these days, but it has always been a bit unpredictable on my iPad. Google’s Drive app is sub-par, and their integration with the Files app not much better. Expect things to be a bit odd compared to how you expect them to work.
If this does not work for you, try to be more specific abaout what you are trying to do, and how you are attempting it. we might be able to offer more specific advice.