about Nedit 5.2 (RC1, i386 linux)
nedit -read <file>
nc -read <file>
Opening a file with the -read option causes nedit to open the file in 'read-only' mode, regardless of the file permissions. That's what the documentation says and that's what is does now.
However a file with write permissions should be opened in 'locked' mode instead, because in 'read-only' mode it's not possible to switch to 'edit' mode in the Preferences menu. The only way to modify the file is to close and reopen it.