How to open pdf file new tab in browser in ASP.NET C#

When select an item from dropdownlist it will open a file in new tab. There is no error. but when I click on link button,click event does not fire of link button.

Again dropdownlist SelectedIndexChanged event is fired when I click on link button.

When I select from dropdownlist , it open a file new tab but dows call javascript function "ResetTarget()"

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
"BodyContent" ContentPlaceHolderID="MainContent" runat="server">
"text/javascript">
function ResetTarget()
{
alert('Yes');
document.forms[0].target = '';
}
function SetTarget()
{
document.forms[0].target = "_blank";
window.setTimeout("document.forms[0].target='';", 500);
}
"hidCSRF" runat="server" Value="" />
"center" class="SubFormWOBG" style="line-height: 25px; width: 100%">
"width: 40%">Application Code:
"width: 60%">
"lnkApplicationCode" runat="server" CausesValidation="false" OnClick="lnkApplicationCode_click">
"server" id="MandatAtt">
Mandatory Attchment:
"server" ID="ddlAttachment" AutoPostBack="true" OnSelectedIndexChanged="ddlAttachment_SelectedIndexChanged">

in c# file

protected void Page_Load(object sender, EventArgs e) {
if (!IsPostBack) {
try {
lnkApplicationCode.Text = "135";
MandatAtt.Visible = false;
ddlAttachment.Attributes["onchange"] = "SetTarget();";
MandatAtt.Visible = true;
} catch(Exception) {
Response.Redirect("~/ErrorPage.aspx", false);
} finally {}
}
}
protected void ddlAttachment_SelectedIndexChanged(object sender, EventArgs e) {
try {
string[] arr = ddlAttachment.SelectedValue.ToString().Split(',');
int int_attachmentCode = Convert.ToInt32(arr[0]);
int int_attachmentSerialCode = Convert.ToInt32(arr[1]);
NOCAPInternalUtility.INDAppViewFiles(Convert.ToInt64(lnkApplicationCode.Text.Trim()), int_attachmentCode, int_attachmentSerialCode);
} catch(System.Threading.ThreadAbortException ex) {} catch(Exception) {
Response.Redirect("~/ErrorPage.aspx", false);
} finally {
hidCSRF.Value = Convert.ToString(System.Guid.NewGuid());
ViewState["CSRF"] = hidCSRF.Value;
ScriptManager.RegisterStartupScript(this, GetType(), "function", "ResetTarget();", false);
}
}
protected void lnkApplicationCode_click(object sender, EventArgs e) {
hidCSRF.Value = Convert.ToString(System.Guid.NewGuid());
ViewState["CSRF"] = hidCSRF.Value;
try {
long ApplicationCode = Convert.ToInt64(lnkApplicationCode.Text);
Session["ApplicationCode"] = ApplicationCode;
} catch(Exception) {
Response.Redirect("~/ErrorPage.aspx", false);
}
}