On the products page of the app, choose a product and press the manage button.
In the top right hand corner of the selected product sits a button called 'Set custom search attribute'
Click this, and it will open a popup where you can type the custom code.
(We will look to add bulk uploading for this shortly)
For the time being, you would need to do this for each product that you have a custom search term for.
Then, head over to the widgets page, and choose the 'Manuals List' widget.
Within this page, scroll down to the section called 'Table Features' where you will find two new attributes. One for the width of the custom search attribute column, and one for showing or hiding this column.
Make sure its turned on to 'show'.
Then load the manuals list page within your site, and you should see the new column with the relevant search term for each product you've set.