You can run the converter in the security context of another user using the properties of an Winnovative.ImpersonationOptions object exposed by the HtmlToPdfConverter.ImpersonationOptions property.
If you already set <identity impersonate="true" /> in the Web.config file of your ASP.NET application to impersonate to another user then you also have to configure the converter to run in the same security context by setting the ImpersonationOptions.CurrentUserImpersonation property on true before running the converter.
If you simply want to run the converter in the security context of another user, eventually more privileged, you can specify the user credentials using the ImpersonationOptions.Username, ImpersonationOptions.Password and ImpersonationOptions.Domain properties.