When you open a text file in Notepad on Windows, you can move the source file to the Recycle Bin or even permanently delete it. The same is true for WordPad. Why is it that Windows doesn't give you a warning, complaining about file being open in another program?
However, if the same file is open in Word, and you try to moved the source file to the recycle bin or delete it permanently, Windows does give you a warning. The message itself can be a warning type of message, telling you that some (often unknwon) program has the file open. In case of Word 2013 on Windows 8.1 this is an info message, telling you exactly what program (Word) has the file open.
Why is that? Why is it that you can A) delete the source file while it's open in a program, and B) continue working on the document after the file has been deleted? Why is the behavior different in Notepad and WordPad from that of Word?
The first case behavior exists in Paint too. You can delete a bitmap file while it's open in Paint and continue working. But when you try to save it you get prompted for file location to save it to. With Notepad, it directly saves it to the same location that the original file was stored in and gives it the same name. Notepad doesn't prompt you for that.
I have not tested this on Windows 7, Vista, or XP. However, I would expect the behavior to be exactly the same, and so the question would probably apply to those systems as well.