You need to create an Output preset in the designer that you will select and use in the Create Output plugin. For simple PDF output I have a plugin I call Generic PDF. Output presets can be made in File-Print Presets-Output Creation Settings. In this section you can specify where the file must go when output in Workflow. If you set it as Prompt For File Name then in Workflow you must select the Through Workflow radio button in the Create Output properties and then a send to folder or Printer Queue or Print Using a Windows Driver plugins. (Depending on what you want I guess)
I would suggest to send via LPR using the Printer Queue plugin or you can have an Output Preset that sends the file to a LPR Queue. But you would have to have selected LPR Queue when creating the Output Preset and drag and drop the Create Output Plugin to where you normally see a send to folder. You can also use the All In One plugin as an output too which can be faster.