If the company has proper license you should be able to obtain the Telerik UI for ASP.NET AJAX suite by logging in with credentials of the license holder and navigating to the download section of the account. If you need more details about account matters you can contact our sales team via firstname.lastname@example.org
To get started with the RadEditor I suggest following the online documentation
as best explains the needed basic steps to configure a project with a RadEditor control.
To setup the PDF exporting functionality you can follow this article
and this online example
The exception thrown is quite self-descriptive. As the error message states, the XHTML that is invalid and due to that the PDF exporting library throws the exception.
I suggest checking the validity of the HTML content used via the W3C validation tool
. If any errors are found, I suggest correcting them, so that you could be sure that correct and valid HTML is used in the Radeditor control.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.