Add prefix in every line of notepad & same automatic process in all multiple notepads

I Have 40,000 Different notepad files in a folder I Want To add Prefix in every line of notepad & Do same for 40,000 files how ??? I cannot do Huge Big Work open each file and adding prefix(will takes month's) I know to add prefix in notepad++ But I have 40,000 files ,to do,I Will die .guys Any tricks or software,..,So I can do it all ones ?? {So To Save Time & Money} Guide Me Guys?