How to get delivery order header text in 'VL01N'?

To read header text in any Transaction no need to go for user exit.
Go to VL02N and goto header details and select menu path GOTO-->HEADER-->TEXTS.You will get Texts details screen.
Just double click on the screen.It takes u to Text editor.
Then select menu path GOTO--> HEADER.
You will receive
1) TEXT NAME
2)LANGUAGE
3)TEXT ID
4)TEXT OBJECT
details.
Then in abap program by using READ_TEXT FM by passing above parameters u can read out text.
Hope this will work out.