When sending commercial mail from the UK which has a value over £270 then you must include a customs form CN22. This plugin integrates with WooCommerce by adding an action to the orders page to print the CN22 form.
For the CN22 form to collate the correct information you will need to ensure that the shipping weight is set for each product else the weight will be 0.
This screen shot description corresponds to screenshot-1.png. This shows the new action in the Order page.
This screen shot description corresponds to screenshot-2.png. This shows the CN22 form.