Load a pdf on button click

Hello,
I have a situation where I need to take a input value and bring a different value from the database and then based on the retunr value, load a pdf. I am not able to make the pdf laod. any suggestions??
HTML code:
<asp:textbox id="txtUserid" runat="server" Width="112px" MaxLength="50"></asp:textbox>
<asp:button id="btnSubmit" runat="server" Text="Submit"></asp:button>
Code behind:
ID = txtUserid.Text
'Search Datbase based on the value of ID and find the zipcode for the person. then load the pdf for the particular zipcode
'Datbase search code goes here and then the belwo code follows
If sZipCode = '10041' Then
    btnSubmit.Attributes.Add("onClick", "javascript:window.open('/zipcodes/pdf/zip10041.pdf');")
else if sZipCode = '079 ...