Packing slips can be edited in Settings > Shipping and delivery > Edit packing slip template
You’ll need to add the code below on line 126 to between the code for {% endif %} and {% if line_item.sku != blank %} (see screenshot for the exact placement):
{% for p in line_item.properties %}
{% unless p.last == blank %}
<div class="item-description-line">{{ p.first }}:
{% if p.last contains '/uploads/' %}
Uploaded File
{% else %}
{{ p.last }}
{% endif %}</div>
{% endunless %}
{% endfor %}Example:
Click the link below if you want to use Shopify’s Order Printer App.