Create a column in the advanced PDF template and add the column with HS code populated from the item record.
SOLUTION
Generated a new field within the item record dedicated to HSN codes and input the provided HSN code into the item records corresponding to the items listed in the invoice.
Generated a new field within the invoice record dedicated to HSN codes and sourced the field from the item record with source list as HSN code field in the item record.

Integrated an additional column into the Invoice PDF to accommodate the HSN code and source the value from invoice record in the sales order
<table class="itemtable" style="width: 100%;"><!-- start items --><#list record.item as item><#if item_index==0>
<thead>
<tr>
<th colspan="6">${item.item@label?upper_case}</th>
<th colspan="7">${item.description@label?upper_case}</th>
<th align="center" colspan="4"> HSN<br />CODE</th>
<#if tax_amt>
<th colspan="4">${item.tax1amt@label?upper_case}</th>
</#if><#if tax_rate><!-- <th colspan="2">${item.taxrate1@label?upper_case}</th> -->
<th align="center" colspan="3"> TAX<br />RATE</th>
</#if><!-- <th align="center" colspan="3">${item.quantity@label?upper_case}</th> -->
<th align="center" colspan="2" line-height="150%">QTY</th>
<th align="center" colspan="5">${item.rate@label?upper_case}</th>
<th align="center" colspan="5">${item.amount@label?upper_case}</th>
</tr>
</thead>
</#if><tr style="background-color: <#if (item_index % 2) == 0>#ffffff<#else>#e1e6ee</#if>">
<td colspan="6">${item.item}</td>
<td colspan="7">${item.description}</td>
<td colspan="4">${item.custcol_jj_hsn_code_id}</td>
<#if tax_amt>
<td colspan="4">${item.tax1amt}</td>
</#if><#if tax_rate>
<td align="center" colspan="3">${item.taxrate1}</td>
</#if>
<td align="center" colspan="2" line-height="150%">${item.quantity}</td>
<#if item.rate?length != 0 ><#assign localcurrency = item.rate?string[0] /><#elseif item.amount?length != 0 ><#assign localcurrency = item.amount?string[0] /><#else><#assign localcurrency = "$" /></#if><#assign rateval = item.rate?string(",##0.00") /><#assign amtval = item.amount?string(",##0.00") />
<td align="right" colspan="5">${localcurrency}${rateval}</td>
<td align="right" colspan="5">${localcurrency}${amtval}</td>
</tr>
</#list><!-- end items --></table>