I have a couple of files which I have to update periodically through a process written in VB.net . 
These files are on a server and part of a domain that many users can access. These files should never be written to as they are for reference only. I need to be able to overwrite some of them even if a user has them opened. Is it possible to do this? Presently the files permissions are not set as read-only but I can do this as long as the user under which the process runs will still have permission to overwrite them.

UPDATE: thx for your responses. The files are pdf and are opened by clicking on them from windows file explorer. This also happens when a user simply has the file selected in windows explorer.