Actually, when occurs an exception with the viewer, the users are seeing a message containing the stack trace of the exception.
Thank you for your proposition, it is a quite fair and reasonable suggestion, we added it to our roadmap.
We will notify you when it will be implemented.
The last version of the GroupDocs.Viewer - 2.6.0 - already contains this feature. Please specify the
Groupdocs.Web.UI.Viewer.ShowExceptionDetailsOnClient(true) or Groupdocs.Web.UI.Viewer.ShowExceptionDetailsOnClient(false) in order to enable or disable the exception details on the client-side.
If you will have more questions please feel free to contact us.