Custom Error page in Event Receivers for SharePoint 2013

Following steps for Custom Error Page.

1. Update the Event Receiver: ItemAdding Section's Code would be:

public override void ItemAdding(SPItemEventProperties properties)

       {

          base.ItemAdding(properties);

           if (!properties.AfterUrl.EndsWith("pdf"))

           {

               properties.Status=SPEventReceiverStatus.CancelWithRedirectUrl;

               properties.RedirectUrl = "/_Layouts/ERTest/ApplicationPage1.aspx";

           }

       }
2. Add a Application Page to the Project, optionally a Icon to represent Error.

3. Update the Error page: Under the PlaceHolderMain Place some content to give descriptive Error message:

See the Result in action: SharePoint 2010 event receiver custom error page.