How to upload arbitrary files to iCloud

iCloud provides you 5GB free for each Apple ID. However, it’s rather difficult to use the free storage because Apple only allows to upload document files. If you want to upload other file types, you can follow the steps below.
First, compress the file (or folder) you want to upload to iCloud. In Windows, right click on the file (or folder) > Send to > Compressed, e.g. to compress file CamStudio20.zip:

Then, open iCloud in browser, log in with your Apple ID and choose iWork.

Rename CamStudio20.zip to CamStudio20.zip.ppt if you choose Keynote (or .doc if you choose Pages). Choose Yes if Windows asks whether or not you want to change file extension.

Click on the icon on the top right corner and choose Upload.

Browse to the file and upload.
Done!