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

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C#

ASP.NET

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()"

What I have tried:

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>


<asp:Content ID="BodyContent" ContentPlaceHolderID="MainContent" runat="server">
    <script type="text/javascript">
        function ResetTarget() {
            alert('Yes');
            document.forms[0].target = '';
        }
        function SetTarget() {
            document.forms[0].target = "_blank";
            window.setTimeout("document.forms[0].target='';", 500);
        }

    </script>
    <asp:HiddenField ID="hidCSRF" runat="server" Value="" />
    <table align="center" class="SubFormWOBG" style="line-height: 25px; width: 100%">
        <tr>
            <td style="width: 40%">Application Code:
            </td>
            <td style="width: 60%">
                <asp:LinkButton ID="lnkApplicationCode" runat="server" CausesValidation="false" 
                     OnClick="lnkApplicationCode_click"></asp:LinkButton>
                
            </td>
        </tr>

        <tr runat="server" id="MandatAtt">
            <td>Mandatory Attchment:</td>
            <td>
                <asp:DropDownList runat="server" ID="ddlAttachment" AutoPostBack="true"
                    OnSelectedIndexChanged="ddlAttachment_SelectedIndexChanged">
                </asp:DropDownList>

            </td>
        </tr>
    </table>

</asp:Content>

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);
            }
        
    }