How can i get download link with watin?

Question

There is a HTML code, in another website :

<form action="down.php" enctype="multipart/form-data" method="post">
    <input type="hidden" name="mid" id="mid" value="pg/K/c3scJubYvZj8UI=" />
    <span><input class="btnff" type="submit" value="downloadd" /></span>
</form>

I want to download with Watin and c sharp :

 WatiN.Core.Button btn1 = browser1.Button(Find.ByValue("downloadd")) as WatiN.Core.Button;
                    btn1.Click();

When I click on it, download start with IDM(Internet download manager). The Link does not exist in Source code, even after I click on Button.

How can I get Link with Watin(Not IDM) and download with c sharp to save in a specific folder?