use below code you should add
using System.Net;
to run this code
if there any problem then feel free to ask again with specific problem details. and don't forget to show your code.happy coding :)
static void Main(string[] args)
{
using (WebClient wc = new WebClient())
{
wc.DownloadFile("http://www.kanpuruniversity.org/SYLLABUS/BSc_Biotech_%20Single_Subject.pdf", "c:\\Single_Subject.pdf");
}
}