I'm trying to do this as well.  I've created a PDF Template with a fillable pdf, mapped fields to a table, then pointed the HR Case Template "PDF Template" fields to the PDF Template I created.  Then I went and created an HR Task that is of type "HR Service" and pointed it to the HR Service that maps to the HR Case Template.  Then I have an lifecycle event that has several activity sets, one of which has an activity that points to the HR Task Template I created.  When I create a new case using the lifecycle event HR Service that I've created seperately, all of the tasks generate properly, but when I go to the fillable PDF Task, it simply displays "You are either not authorized or record is not valid.".   I've watched this video https://www.servicenow.com/community/hrsd-articles/advanced-forms-management-in-hr-service-delivery/... - about 20 times.  What she doesn't show is the Record Producer associated with the HR Service or how it is created - so I think that's where I'm going wrong.  She has a record producer associated with the HR Service and I do not.  When I add one, it displays whatever record producer I select.... but in her video she get's a nice fillable PDF at the end.  Gaaaaah.