[SharePoint] Fix Attachment in New Form when the form was using Custom List Form

SharePoint New Form from a List

If a new form was created by using custom list form method (SharePoint Designer => Insert => SharePoint Controls => Custom List Form...)

When form is opened and users try to use the attachment function (Attach File), they received a warning "This form was customized not working with attachment."

To fix it, open the form in Code View,

Search for:
<table border="0" width="100%">
<xsl:call-template name="dvt_1.body">
<xsl:with-param name="Rows" select="$Rows"/>
</xsl:call-template>
</table>

Replace with:
<div>
<span id="part1">
<table border="0" width="100%">
<xsl:call-template name="dvt_1.body">
<xsl:with-param name="Rows" select="$Rows"/>
</xsl:call-template>
</table>
</span>
<SharePoint:AttachmentUpload runat="server" ControlMode="New"/>
<SharePoint:ItemHiddenVersion runat="server" ControlMode="New"/>
</div>


In bottom of the form, look for:
<xsl:if test="$dvt_1_automode = '1'" ddwrt:cf_ignore="1">
<tr>
<td colspan="99" class="ms-vb">
<span ddwrt:amkeyfield="ID" ddwrt:amkeyvalue="ddwrt:EscapeDelims(string(@ID))" ddwrt:ammode="view"></span>
</td>
</tr>
</xsl:if>

Add code before/above those codes:
<tr id="idAttachmentsRow{''}">
<td width="190px" valign="top" class="ms-formlabel">
<H3 class="ms-standardheader">
<nobr>Attachments:</nobr>
</H3>
</td>
<td valign="top" class="ms-formbody" width="80%">
<SharePoint:FormField runat="server" id="AttachmentsField" ControlMode="New" FieldName="Attachments" __designer:bind="{ddwrt:DataBind('i','AttachmentsField','Value','ValueChanged','ID',ddwrt:EscapeDelims(string(@ID)),'@Attachments')}"/>
<script>
          var elm = document.getElementById("idAttachmentsTable");
          if (elm == null || elm.rows.length == 0)
          document.getElementById("idAttachmentsRow").style.display='none';
        </script> </td>
</tr>