The best way to extract data from a website and show small parts in an app?

I'm trying to think best way to see in another web or in another app, only some parts of another web. Tryed to download html and parse it but not useful becouse ajax parts don't update the needed info. thinked about use in .net a browser, make some frames, and load all webpages into each, but this eats a lot of resources.

Any idea? javascript must be run for ajax.

thank you and sorry for first message asking, lost my old account.