Symptoms

When firing off the PDF Converter against a form url with a Worklist control on said form, the PDF rendered/saved would be of just the loading page with the little green spinner.
 

Diagnoses

The reason that happens is because the PDF Convert Service executes under the context of the service account and the worklist control executes under the context of some user account. This setup is trying to pass the service account credentials to the worklist control which is not a good set up.

 

Resolution

To dodge that issue you can simply create a form state that does not have the worklist control on it and feed in that URL to the PDF Converter.