Since you could not copy that file, everything else failed.

Just be sure you are in the right place. When saving the file, put it on the very root of your device memory. Even if, from the point of view of the browser you are in the root, you really are inside the directory /home/user/MyDocs. At this point don't be confused by the Documents directory. That directory is inside /home/user/MyDocs.

Also, after you type the sudo gainroot, do not move from /home/user, all commands must be run from that place.