Try this
String strPop = "<script language='javascript'>" + Environment.NewLine +
"window.open('C:\MyWork\Test\TestFile\test.pdf"','Report','height=520,width=730,toolbars=no,scrollbars=yes,resizable=yes');" + Environment.NewLine +
"</script>" + Environment.NewLine;
Page.RegisterStartupScript("Pop", strPop);