To enable a user to both read and write to a file, the administrator needs to provide "modify" rights. This permission level allows the user not only to open and view the file (read) but also to make changes and save those changes back to the file (write). "Read and execute" rights would allow the user to open and run the file but not make any changes. "List folder contents" rights would enable the user to view the files within a folder but not make changes to them. "Full control" rights would provide the user with complete control over the file, including the ability to change permissions and delete the file, which exceeds the principle of least-privilege access necessary for this task.