For forwarding email, you have to set things up at the source end, not at icloud.
iCloud doesn't pick up documents, it's the programs and apps that do the syncing. For example, Pages can save docs to icloud and do that automatically whenever you edit a file saved there. (But for a PC, there may be fewer, if any, programs that use icloud.)
iCloud is not designed like Dropbox, that's a different kind of service.