Problem

Validation of a WSDL using Eclipse WSDL Explorer tool

Resolution

You need to install the correct version of Web Tools Platform

http://www.eclipse.org/webtools/

Then there are some instructions for validating a WSDL with the Web Services Explorer here:

Testing WSDL documents and Web services using the WSDL Explorer

Note file WSDL URL on Windows works like this ... file:///C:/Users/Martin/Downloads/handleEmailBounces.wsdl