Show PDF on CheckedChanged

I have a form that has a check box and when check I would Like to pass the PDF to download to the next page.
I am going to store the PDF's in a folder and retrieve for the folder.

I am not sure how to do this Does anybody now of any tutorials or how this is done.
This is where I'm at  

protected void chk_Form_E_CheckedChanged(object sender, EventArgs e) {
}