Source page:
<form method="POST" action="path/to/other/page.aspx" target="_blank">
<p>
<label for="Name">Name:</label>
<input type="text" id="Name" name="Name" placeholder="Your name" />
</p>
<p>
<input type="submit" />
</p>
</form>
Target page:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
string name = Request.Form["Name"];
...
}
}