You have created a custom jaspersoft report and need the report PDF export to default to the Project Name as the file name,
Release : Clarity 15.9.1, 16.1
Jaspersoft: 7.13, 7.8
Unfortunately, this is not possible. TIBCO has had requests for that as an enhancement request
https://jaspersoftideas.tibco.com/ideas/JSPR-I-4363
https://jaspersoftideas.tibco.com/ideas/JSPR-I-4571