There are many independent software solutions out there, for a nominal fee.
If you have the full version of Acrobat, you can make use of their API as
well. The only free way I know of is to use a PHP script. There are
examples on how to do this. PHP will run alongside .NET on the server,
there are guides on how to do this as well.
Not the simplest of items to install and make work on deployment, but
Visual Studio comes with a minimal version of Crystal Reports that can
generate PDF files - even streaming them to the browser with the
correct incantations.