Protect a range of cells remotely from another file
 

I have a number of individual files and equal number of people who have
access to each of their own file. I have access to all their files and data.
They enter information every month and it gets summarized into my
spreadsheet. Once they enter their data and after I look at it, I don't want
them to change it again. How do I do it without having to go to individual
files and protecting the specific range of cells?