To alter the invoice product table row height (https://www.webtoffee.com/product/woocommerce-pdf-invoices-packing-slips/)

functions.php

<?php // do not copy this line of code
add_filter('wf_pklist_add_custom_css','wf_pklist_alter_line_height',10,3);
function wf_pklist_alter_line_height($custom_css, $template_type, $template_for_pdf)
{
	if($template_type=='invoice')
	{
		//You can specify the line-height from below
		$custom_css.='.wfte_product_table_body .product_td b{line-height: 6px !important;}';
		if($template_for_pdf)
		{
			$custom_css.=".wfte_product_table_body .product_td b{line-height: 6px !important;} ";
		}
	}
	return $custom_css;
}