Hi,
Operating under the assumptions :
1. It's an xfa based pdf which you want to render as HTML Form instead of PDF form.
2. It's AEM Forms 6.0 or greater version.
Please perform following steps :
1. Go to "Action Profile" in "Startpoint" and/or "Task" properties in workbench.
2. Select "HTML" under "Default render process configuraions".
3. Save the changes and deploy app.
Your form should now be rendered as HTML.
Please, let me know if any of my assumptions doesn't hold in your case or if you continue to face issues or need further instructions in steps to be performed.