The external end user wants to download the API document from API portal. Does API portal support document download ?
If an API owner added a WSDL file for the API on the Portal, then developers can download the API's documentation by going to the Portal's Documentation page, selecting the API, and then clicking Download Documentation.
http://<yourgateway>:<port>/<API>?wsdl
I don't believe there is currently a way to do this with a WADL (or I haven't had success in doing so). However, if you publish a SOAP API from the API Portal (Portal Published API) and add a WSDL and a path for a documentation page, you should see a button for "Download Documents" on the documentation page associated with that API.
Regards,
Azad