If a user has PDF reader installed in his machine, he can directly view your pdf link. For ex -
http://www.cheat-sheets.org/saved-copy/aspnet-life-cycles-events.pdf[
^]
You will be able to open this of you have pdf reader installed. If you need a custom viewer which should work even without client having PDF reader installed, you will have to write code to implement one. There are already lot of examples on web how to implement it -
Google search - Show PDF file asp.net[
^]. Not sure how you couldn't find anything.