Documents created with some third party application say Microsoft office will again sync see this article https://support.apple.com/en-us/HT207428
And a link https://discussions.apple.com/docs/DOC-13681
See this article also https://support.apple.com/en-in/HT201104
What types of files can I store in iCloud Drive?
You can store any type of file in iCloud Drive, as long as it's 50GB or less in size and you don't exceed your iCloud storage limit. That means you can keep all of your work documents, school projects, presentations, and more up to date across all of your devices. Learn more about managing your iCloud storage.
You shouldn't store app folders, libraries, or .tmp files in iCloud Drive.
And as per this article https://support.apple.com/kb/PH19386?locale=en_US
With iCloud Drive, you can securely store your files in iCloud, and access them on iCloud.com and all your computers and iOS devices. With macOS Sierra or later, you can have all the files in the Desktop and Documents folders on your Mac stored automatically in iCloud Drive. That way, you can save files right where you usually keep them on your Mac, and they become available on iCloud.com and all your computers and iOS devices.
If you had created a folder in www.icloud.com and transferred some files in it https://support.apple.com/kb/PH27914?locale=en_US&viewlocale=en_US
note : it depends what way you signed out from iCloud and again signed in , and you had turned on iCloud Drive https://support.apple.com/en-in/HT204025
And the box of desktops and documents was checked see this https://support.apple.com/en-us/HT206985