Form Runner can produce PDF files in two ways:
Automatically. The PDF is produced based on the appearance of the form in your web browser. This is similar to printing a read-only version of your form. See also Automatic PDF.
From PDF templates. You upload one or more PDF files using the “Attach PDF Templates” dialog. At runtime, Form Runner fills-out Acrobat fields in the template. See also PDF Templates.
Since Orbeon Forms 2018.1, you can attach more than one PDF template to a form definition. Templates are differentiated by a name and/or a language, which you specify when attaching the PDF.
When producing the PDF at runtime, as part of a “Send” or “Submit” process,  you can specify a name to pick from the available PDF templates. Then the form’s current language is used to pick from the remaining PDF templates, if they specify a language.
This enables two types of scenarios. The first one is that you can have localized PDF templates. Say your form supports English and Spanish, then you can have a PDF template in English and a PDF template in Spanish, and the appropriate PDF will be used depending on the language of the user.
The second scenario consists in producing different PDFs depending on which button the user is activating, or depending on specific data in the form. For example, you could produce both a short summary PDF, and a full PDF with all the information captured with the user.
Along with this change to PDF templates you can also decide, in a process, to use the automatic PDF instead of a PDF template, even if one or more templates are present. This provides you with more flexibility for PDF production.