Do you have the attachment option enabled in the plugin? It should be showing up wherever you put the attachment variable in the form template. The default example looks like this:
Code:
<if condition="$attachmentoption">
<tr>
<td class="alt1" colspan="3" align="center">
<div style="width:$stylevar[formwidth]" align="$stylevar[left]">$attachmentoption</div>
</td>
</tr>
</if>