saving a file put a blank file on desktop

My son had two very important exams today and was allowed by the Ministry of Education to use his personal computer to key in his answers. He saved his file(s) multiple times onto the desktop. But when the school authorities checked his file(s) they were blank (0 octets). Does the app or computer have the text hidden somewhere in the root? Many thanks for your invaluable help on this matter.

Missing information. What operating system? What type of file? Were they looking at the file or looking at a link to the file?