You can create a custom mapping that uses sendinc.com for the WS call. Read up your pdf and then attach it to a WS call that will handle the attachment for you.
var emailTo = 'xyz@email.com,123@email.com';
var fileBytes = qie.readFile('filepath');
var parameterMap = qie.newParameterMap();
parameterMap.put('http.header.encoding', 'ISO-8859-1');
var urlTemplate = qie.evaluateTemplate('https://rest.sendinc.com/message.xml');
var content = ('Content-Type:multipart/form-data; boundary=AaB03x\n'+
'\n'+
'--AaB03x\n'+
'Content-Disposition:form-data; name=\'email\'\n'+
'\n'+
'abc@example.com\n'+
'--AaB03x\n'+
'Content-Disposition:form-data; name=\'recipients\'\n'+
'\n'+
emailTo + '\n'+
'--AaB03x\n'+
'Content-Disposition:form-data; name=\'subject\'\n'+
'\n'+
'Test Message\n'+
'--AaB03x\n'+
'Content-Disposition:form-data; name=\'message\'\n'+
'\n'+
'This is a Test Message \n'+
'--AaB03x\n'+
'Content-Disposition:inline; name=\'file\'; filename=\'1.pdf\'\n'+
'Content-Type:application/pdf\n\n'+
new java.lang.String(fileBytes, 'ISO-8859-1')+ '\n' +
'--AaB03x--\n');
var value = qie.callRESTWebService('asendinc', urlTemplate,'POST',content,'multipart/form-data;boundary=AaB03x',parameterMap);
