This order form contains input/text line-item sections (e.g. if you wanted an order form with custom engraving). A simple way to implement is to create a collection with duplicate Item names.

Shopify Fillable Order Form

{% comment %}
Source: https://gist.github.com/carolineschnapp/9122054
If you are not on a collection page, do define which collection to use in the order form.
Use the following assign statement, replace 'your-collection-handle-here' with your collection handle.
{% assign collection = collections.your-collection-handle-here %}
Use the assign statement outside of this comment block at the top of your template.

Big thanks to this post for pointing me in the right direction: https://community.shopify.com/c/Shopify-Design/Order-Form-and-Line-Item-Properties/m-p/388892
{% endcomment %}


{% paginate collection.products by 100 %}

{% if collection.products_count > 0 %}
<div class="action-bar top clearfix">
  <h1 class="left">{% if template contains 'page' %}{{ page.title }}{% else %}{{ collection.title }}{% endif %}</h1>
  <input class="action-button submit button btn right add-to-cart-order-form" type="button" value="Add to the cart" />
</div> 
{% else %}
<h1>{% if template contains 'page' %}{{ page.title }}{% else %}{{ collection.title }}{% endif %}</h1>
{% endif %}

{% if template contains 'page' and page.content.size > 0 %}
<div class="rte">
{{ page.content }}
</div>  
{% elsif collection.description.size > 0 %}
<div class="rte">
{{ collection.description }}
</div>
{% endif %}

{% if collection.products_count > 0 %} 
{{ 'http://yui.yahooapis.com/pure/0.4.2/tables-min.css' | stylesheet_tag }}
<table class="pure-table pure-table-bordered">
  <tbody>
  {% for product in collection.products %}
    {% if product.available %}
      {% for variant in product.variants %}
        {% if variant.available %}
        <tr class="{% cycle 'pure-table-odd', '' %}">
          <td>
            <a href="{{ product.url | collection }}">
              <img src="{{ product.featured_image.src | product_img_url: 'thumb' }}" alt="{{ product.featured_image.alt | escape }}" />
            </a>
          </td>
          <td>
            <a href="{{ product.url | collection }}">
             {{ product.title }}{% unless variant.title contains 'Default' %} - {{ variant.title }}{% endunless %}{% unless variant.sku == '' %} - {{ variant.sku }}{% endunless %}
            </a>
          </td>
           <td>
{% comment %}
      below you add the input box, note that variant.id is required       
{% endcomment %}             
             <input id="{{ variant.id }}" name="headerprop" value="" type=text>
  </td>
          <td style="text-align:right;">
            <input onfocus="this.select()" class="quantity field" data-id="{{ variant.id }}" min="0" {% unless item.variant.inventory_management == blank or item.variant.inventory_policy == 'continue' %}{% assign max = variant.inventory_quantity %}{% for item in cart.items %}{% if item.id == variant.id %}{% assign max = max | minus: item.quantity %}{% endif %}{% endfor %} max="{{ max }}" {% endunless %} type="text" value="0" tabindex="1" />
          </td>
        </tr>
        {% endif %}
      {% endfor %}
    {% endif %}
  {% endfor %}
  </tbody>
</table>
<div class="action-bar clearfix">
  <input class="action-button submit button btn right add-to-cart-order-form" type="button" value="Add to the cart" />
</div> 
{% else %}
<p>There are no products in this view.</p>
{% endif %}

{% endpaginate %}

{% if collection.products_count > 0 %}
<script>
Shopify.itemsToAdd = [];
Shopify.addItemstoTheCart = function() {
  if (Shopify.itemsToAdd.length) {
    var item = Shopify.itemsToAdd.pop();
    $.ajax({
      url: '/cart/add',
      dataType: 'json',
      type: 'post',
      data: item,
      success: Shopify.addItemstoTheCart,
      error: Shopify.addItemstoTheCart
    });
  }
  else {
    window.location.href = '/cart';
  }
};
jQuery(function($) {
  $('table .quantity:first').focus();
  $('[max]').change(function() {
    var max = parseInt($(this).attr('max'), 10);
    var value = parseInt($(this).val(), 10) || 0;
    if (value > max) { 
      alert('We only have ' + max + ' of this item in stock');
      $(this).val(max); 
    }    
  });
  $('.add-to-cart-order-form').click(function() {
    $('.add-to-cart-order-form').addClass('disabled').attr('disabled','disabled');
    // Resetting.
    Shopify.itemsToAdd = [];
    $('.quantity').each(function() {
      var quantity = parseInt($(this).val(), 10);
      if (quantity) {
         testid = "#"+ $(this).attr('data-id');
      Shopify.itemsToAdd.push( { id: $(this).attr('data-id'), quantity: quantity, properties: {
     Input: $(testid).val() //this is where you change how the item is described in the cart and where the input is grabbed from
  }
      }
                             ); }});     
    if (Shopify.itemsToAdd.length) {
      Shopify.addItemstoTheCart();
    }
    else {
      alert('All quantities are set to zero.');
      $('.add-to-cart-order-form').removeAttr('disabled').removeClass('disabled');
    }
  });
});
</script>
{% endif %}
  
<style>
.action-bar { margin: 15px 0; }
.action-bar.top { margin: 30px 0 0; }
.action-bar h1 { margin:0; padding: 0; line-height:1 }
.left { float: left; }
.right { float: right; }
.clearfix:before, .clearfix:after { content: ""; display: table; }
.clearfix:after { clear: both; }
.clearfix { zoom: 1; }
/* Additional styles for table */
table.pure-table { margin: 15px 0; width: 100%; }
table.pure-table tr td:first-child, table.pure-table tr th:first-child { padding-left: 12px; }
table.pure-table tr td:last-child, table.pure-table tr th:last-child { padding-right: 12px; }
table.pure-table img { float:left; padding: 5px 0; }
table.pure-table td { vertical-align: middle; }
.quantity { text-align: center; width: 60px !important; margin: 0 !important; }
</style>