Document Publisher - Source item fields

I am trying run Document Publisher at a Request Leve l" Publish Case Document" CA

I want to use Case ( Request) Source item fields as placeholders that will be replaced with field values.

It working when a do similar document at Project Level for CA "Publish Workitem Document" with project Source item fields as place holders that get replaced with field values.

Project is listed as Source item fields - Can Cases( Requests) used as Source items similarly or NOT?