Custom properties inside SOLIDWORKS are a great way to automate properties between parts/assemblies and drawings. There is an automatic list of properties to choose from, but there are custom properties that might not be in the list.
There are two ways to add additional properties for use. You can click on the blank field at the top of the drop-down and type in whatever name you want.
This is good for properties that are used occasionally or only once. If a property is used for many files, it would be better to add the property permanently to the Custom Property List. Instructions for accessing the notepad file can found at: http://blog.cati.com/2015/07/solidworks-where-did-my-custom-properties-list-go.html
Chad Whitbeck, CSWP
Applications Engineer, CATI