If you are customizing Sharepoint forms using nintex, you may encounter this issue Internal Server Error Building PDF when you click the print to pdf function. The resolution for this issues are
- Ensure that if your image control links to correct Image URL with in your site collection.
- Custom scripts should be clean and you can remove unwanted scripts if any.
This would ensure that your pdf would be downloaded without any error message.
Happy Sharepointing 🙂