The document preview uses the Primary personal of the account to generate a preview before the actual merge. The preview is a "quick peek" at what the document should look like to help you confirm the right document template is selected. It is not the actual merge, so it will use the Primary persona to fill in data fields. If any other personas are set in the Export options, the final output will reflect those settings once it's run.

To see another persona in the preview when generating a document from an account, then the Primary must be updated on the account: 
  1. Click on Personas
  2. Select the desired Persona.
  3. Mark Primary.
  4. Click Save And... to save the change.
  5. Navigate back to the prior point to Generate a document.
  6. Selected the desired template and the updated Primary persona will preview.