The document manager license key is not mandatory. But if you want to have the ability to run searchs by properties you will need it.
To be able to use properties you have first to request from Solidworks a document manager licence key. It's free but you have to be under subscription from Solidworks. Following this link: Document Manager Key Request you can get your document manager licence key.
With the provided key select the "Change Document ..." button and paste your license key.
Check "Document manager" to enable.
Check "Index properties" to build an index of properties (Allow you to run a search by properties)