Craft Commerce: Upload File Field in Order? I'm looking at Craft Commerce as a possible solution. 

In the order process we want customers to be able to upload a file against their order which can then be accessed by the shop administrators. Is this possible and how would we go about that?

I have been looking through the documentation and seen nothing that clearly demonstrates this (yet!).
This is definitely possible. First create a file field to attach to your order in the control panel. Then create a file input type with a name attribute that uses the field you created name="fields[fieldName]". This would then get sent in the post request to updateCart.

&lt;form method="POST" enctype="multipart/form-data"&gt;
  &lt;input type="hidden" name="action" value="commerce/cart/updateCart"&gt;
  {{ getCsrfInput() }}
  &lt;input type="file" name="fields[fieldName][]"&gt;
  &lt;button type="submit"&gt;Upload file&lt;/button&gt;
&lt;/form&gt;


Then you could show the image on the cart/order using something like the following:

{% if cart.fieldName|length %}
  &lt;img src="{{ cart.fieldName[0].url }}"&gt;
{% endif %}