I'm trying to use widget="pdf_viewer" on form view.

on form view under notebook --> Page section: 

field="certificate" widget="pdf_viewer"

After uploading the pdf files, it's showing content correctly. But if i'm reloading / revisit the records, it can't show the PDF content. Here's the error message :

Message: Unexpected server response (500) while retrieving PDF "http://192.168.1.1:8069/web/content?model=skills.matrix&field=certificate&id=18".