This feature is available for V2 forms only. If you do not have access to the V2 Form Builder and Forms, please read: Enabling V2 Forms
V2 forms are built differently than classic forms -- they contain great new features like sections, repeatable sections, and conditional logic.
V2 forms use V2 documents, which are designed to accommodate these new features (without impacting the way that your existing documents on V1 forms work).
V2 PDF, Word, and HTML documents also have new design and formatting options that give you more control over your documents, and give you new ways to apply your custom branding.
These V2 document types have a new structure that includes sections, and data from Repeatable sections.
Note: These formats will be different from V1, especially once repeatable sections are introduced to a form. If you have integrations using these formats, please carefully note the differences.