I want to put popup message like "Hi, Welcome to this page." only in some of the pages in the course. The popup should automatically come when I open the page. How can it be done ?
I would install and use the Generico filter. One of it's included templates is a Welcome like you want that can be easily modified if it needs to be. I have used it for exactly the purpose you mention. The nice thing is that there are a LOT of available templates that let you you show/do many other things. Another nice thing is that you can place a Generico filter just about any location where you can open the Atto or TinyMCE editors.