Martina
In the example you posted, the first two CCs are linked to the Subject property. You can go to your Document Properties and change the value of the Subject field to verify this. The easiest way to add a CC linked to built-in document property is to go to Insert > Quick Parts > Document Property and pick one.
Linking a CC to a built-in property allows you to copy and paste the CC across documents and each time the CC will display the value of that property in the document where you paste it. The drawback of linking to built-in properties is there is a limit to how many properties you can link to.
You can also link to custom XML but that gets more complicated and I would suggest you use a third-party tool for doing that such as
Content Control Tools