Since app.fromPDFConverters is empty in Reader, the answer is no, it's not
Did you read the documentation of the saveAs method?
yes it says
(Adobe Reader S): This method is available in Adobe Reader for documents that have Save usage
The method is available, but you can only use the converters listed in app.fromPDFConverters. This is a different set of converters in Reader, in fact I think it is empty, but you can check.