No you cannot.
However there is a workaround.
From page 31 of the api documentation (located at http://www.methodintegration.com/self-service-documentation.aspx), strAttachment is "the url of an attachment".
Also note this field is not required and can have an empty string passed in.
What you can do is use the function MethodAPIGetScreenURLV4 to generate a url. This url should be a link into a portal which generates the pdf when it loads.
You can then pass this url into the the email function as the strattachment url.